||This article needs more medical references for verification or relies too heavily on primary sources. (August 2012)|
Child development refers to the biological, psychological and emotional changes that occur in human beings between birth and the end of adolescence, as the individual progresses from dependency to increasing autonomy. Because these developmental changes may be strongly influenced by genetic factors and events during prenatal life, genetics and prenatal development are usually included as part of the study of child development. Related terms include developmental psychology, referring to development throughout the lifespan, and pediatrics, the branch of medicine relating to the care of children. Developmental change may occur as a result of genetically-controlled processes known as maturation, or as a result of environmental factors and learning, but most commonly involves an interaction between the two. It may also occur as a result of human nature and our ability to learn from our environment. Human beings have a keen sense to adapt to their surroundings and this is what child development encompasses. Every child would struggle to find their culture and identity in child development.
There are various definitions of periods in a child's development, since each period is a continuum with individual differences regarding start and ending.
Some age-related development periods and examples of defined intervals are: newborn (ages 0–4 weeks); infant (ages 4 weeks – 1 year); toddler (ages 1–3 years); preschooler (ages 4–6 years); school-aged child (ages 6–13 years); adolescent (ages 13–20). However, organizations like Zero to Three and the World Association for Infant Mental Health use the term infant as a broad category, including children from birth to age 3.
The optimal development of children is considered vital to society and so it is important to understand the social, cognitive, emotional, and educational development of children. Increased research and interest in this field has resulted in new theories and strategies, with specific regard to practice that promotes development within the school system. In addition there are also some theories that seek to describe a sequence of states that compose child development.
Ecological systems theory 
Also called "development in context" or "human ecology" theory, ecological systems theory, originally formulated by Urie Bronfenbrenner specifies four types of nested environmental systems, with bi-directional influences within and between the systems. The four systems are microsystem, mesosystem, exosystem, and macrosystem. Each system contains roles, norms and rules that can powerfully shape development. Since its publication in 1979, Bronfenbrenner's major statement of this theory, The Ecology of Human Development has had widespread influence on the way psychologists and others approach the study of human beings and their environments. As a result of this influential conceptualization of development, these environments — from the family to economic and political structures — have come to be viewed as part of the life course from childhood through adulthood.
Piaget was a Swiss scholar who began his studies in intellectual development in the 1920s. Piaget’s first interests were those that dealt with the ways in which animals adapt to their environments and his first scientific article about this subject was published when he was 10 years old. This eventually led him to pursue a Ph.D. in Zoology, which then led him to his second interest in epistemology.] Epistemology branches off from philosophy and deals with the origin of knowledge. Piaget believed the origin of knowledge came from Psychology, so he traveled to Paris and began working on the first “standardized intelligence test” at Alfred Binet laboratories, this influenced his career greatly. As he carried out this intelligence testing he began developing a profound interest in the way children’s intellectualism works. As a result, he developed his own laboratory and spent years recording children’s intellectual growth and attempted to find out how children develop through various stages of thinking. This led to Piaget develop four important stages of cognitive development: sensorimotor stage (birth to age 2), preoperational stage (age 2 to 7), concrete-operational stage (ages 7 to 12), and formal-operational stage (ages 11 to 12, and thereafter).
Piaget stages 
Sensorimotor: (birth to about age 2)
According to Piaget, when an infant reaches about 7–9 months of age they begin to develop what he called object permanence, this means the child now has the ability to understand that objects keep existing even when they cannot be seen. An example of this would be hiding the child’s favorite toy under a blanket, although the child cannot physically see it they still know to look under the blanket.
Preoperational: (begins about the time the child starts to talk to about age 7)
During this stage of development, young children begin analyzing their environment using mental symbols. These symbols often include words and images and the child will begin to apply these various symbols in their everyday lives as they come across different objects, events, and situations. However, Piaget’s main focus on this stage and the reason why he named it “preoperational” is because children at this point are not able to apply specific cognitive operations, such as mental math. In addition to symbolism, children now begin engaging in pretend play where they begin pretending to be people they are not (teachers, superhero’s), and they may use different props to make this pretend play more real. Some deficiencies in this stage of development are that children who are about 3–4 years old often display what is called egocentrism, which means the child is not able to see someone else’s point of view, they feel as if every other person is experiencing the same events and feelings that they are experiencing. (see “The Three Mountains Task”). However, at about at 7 thought processes of children are no longer egocentric and are more intuitive, meaning they now think about the way something looks instead of rational thinking.
Concrete: (about first grade to early adolescence)
During this stage, children begin developing cognitive operations and begin applying this new thinking to different events they may encounter. Unlike the preoperational stage, children can now change and rearrange mental images and symbols to form a logical thought, an example of this is reversibility in which the child now has the ability to reverse an action just by doing the opposite.
The final stage of Piaget’s cognitive development defines a child as now having the ability to “think more rationally and systematically about abstract concepts and hypothetical events”. Some positive aspects during this time is that child or adolescent begins forming their identity and begin understanding why people behave the way they behave. However, there are also some negative aspects which include the child or adolescent developing some egocentric thoughts which include the imaginary audience and the personal fable. An imaginary audience is when an adolescent feels that the world is just as concerned and judgmental of anything the adolescent does as they are, an adolescent may feel as is they are “on stage” and everyone is a critique and they are the ones being critiqued. A personal fable is when the adolescent feels that he or she is unique person and everything they do is unique. They feel as if they are the only ones that have ever experienced what they are experiencing and that they are invincible and nothing bad will happen to them it will only happen to others.
Vygotsky was a Russian theorist, who proposed the sociocultural theory. During 1920s–1930s while Piaget was developing his own theory, Vygotsky was an active scholar and at that time his theory was said to be “recent” because it was translated out of Russian language and began influencing Western thinking. He posited that children learn through hands-on experience, as Piaget suggested. However, unlike Piaget, he claimed that timely and sensitive intervention by adults when a child is on the edge of learning a new task (called the zone of proximal development) could help children learn new tasks. This technique is called "scaffolding," because it builds upon knowledge children already have with new knowledge that adults can help the child learn. An example of this might be when a parent "helps" an infant clap or roll her hands to the pat-a-cake rhyme, until she can clap and roll her hands herself.
Vygotsky was strongly focused on the role of culture in determining the child's pattern of development. He argued that "Every function in the child's cultural development appears twice: first, on the social level, and later, on the individual level; first, between people (interpsychological) and then inside the child (intrapsychological). This applies equally to voluntary attention, to logical memory, and to the formation of concepts. All the higher functions originate as actual relationships between individuals."
Vygotsky felt that development was a process and saw periods of crisis in child development during which there was a qualitative transformation in the child's mental functioning.
Attachment theory 
Attachment theory, originating in the work of John Bowlby and developed by Mary Ainsworth, is a psychological, evolutionary and ethological theory that provides a descriptive and explanatory framework for understanding interpersonal relationships between human beings. Bowlby’s observations of close attachments led him to believe that close emotional bonds or “attachments” between an infant and their primary caregiver is an important requirement that is necessary to form “normal social and emotional development”.
Erik Erikson 
Erikson, a follower of Freud's, synthesized both Freud's and his own theories to create what is known as the "psychosocial" stages of human development, which span from birth to death, and focuses on "tasks" at each stage that must be accomplished to successfully navigate life's challenges.
Erikson's eight stages consist of the following:
- Trust vs. mistrust (infant)
- Autonomy vs. shame (toddlerhood)
- Initiative vs. guilt (preschooler)
- Industry vs. inferiority (young adolescent)
- Identity vs. role confusion (adolescent)
- Intimacy vs. isolation (young adulthood)
- Generativity vs. stagnation (middle adulthood)
- Ego integrity vs. despair (old age)
Behavioral theories 
John B. Watson’s behaviorism theory forms the foundation of the behavioral model of development 1925. He wrote extensively on child development and conducted research (see Little Albert experiment). Watson was instrumental in the modification of William James’ stream of consciousness approach to construct a stream of behavior theory. Watson also helped bring a natural science perspective to child psychology by introducing objective research methods based on observable and measurable behavior. Following Watson’s lead, B.F. Skinner further extended this model to cover operant conditioning and verbal behavior. Skinner used the operant chamber, or Skinner box, to observe the behavior of small organisms in a controlled situation and proved that organisms' behaviors are impacted on the environment. Furthermore, he used reinforcement and punishment to shape in desired behavior.
Other theories 
In accordance with his view that the sexual drive is a basic human motivation, Sigmund Freud developed a psychosexual theory of human development from infancy onward, divided into five stages. Each stage centered around the gratification of the libido within a particular area, or erogenous zone, of the body. He also argued that as humans develop, they become fixated on different and specific objects through their stages of development. Each stage contains conflict which requires resolution to enable the child to develop.
The use of dynamical systems theory as a framework for the consideration of development began in the early 1990s and has continued into the present century. Dynamic systems theory stresses nonlinear connections (e.g., between earlier and later social assertiveness) and the capacity of a system to reorganize as a phase shift that is stage-like in nature. Another useful concept for developmentalists is the attractor state, a condition (such as teething or stranger anxiety) that helps to determine apparently unrelated behaviors as well as related ones. Dynamic systems theory has been applied extensively to the study of motor development; the theory also has strong associations with some of Bowlby's views about attachment systems. Dynamic systems theory also relates to the concept of the transactional process, a mutually interactive process in which children and parents simultaneously influence each other, producing developmental change in both over time.
The "core knowledge perspective" is an evolutionary theory in child development that proposes "infants begin life with innate, special-purpose knowledge systems referred to as core domains of thought" There are five core domains of thought, each of which is crucial for survival, which simultaneously prepare us to develop key aspects of early cognition; they are: physical, numerical, linguistic, psychological, and biological.
Continuity and discontinuity in development 
Although the identification of developmental milestones is of interest to researchers and to children's caregivers, many aspects of developmental change are continuous and do not display noticeable milestones of change. Continuous developmental changes, like growth in stature, involve fairly gradual and predictable progress toward adult characteristics. When developmental change is discontinuous, however, researchers may identify not only milestones of development, but related age periods often called stages. A stage is a period of time, often associated with a known chronological age range, during which a behavior or physical characteristic is qualitatively different from what it is at other ages. When an age period is referred to as a stage, the term implies not only this qualitative difference, but also a predictable sequence of developmental events, such that each stage is both preceded and followed by specific other periods associated with characteristic behavioral or physical qualities.
Stages of development may overlap or be associated with specific other aspects of development, such as speech or movement. Even within a particular developmental area, transition into a stage may not mean that the previous stage is completely finished. For example, in Erikson's discussion of stages of personality, this theorist suggests that a lifetime is spent in reworking issues that were originally characteristic of a childhood stage. Similarly, the theorist of cognitive development, Piaget, described situations in which children could solve one type of problem using mature thinking skills, but could not accomplish this for less familiar problems, a phenomenon he called horizontal decalage.
Mechanisms of development 
Although developmental change runs parallel with chronological age, age itself cannot cause development. The basic mechanisms or causes of developmental change are genetic factors and environmental factors. Genetic factors are responsible for cellular changes like overall growth, changes in proportion of body and brain parts, and the maturation of aspects of function such as vision and dietary needs. Because genes can be "turned off" and "turned on", the individual's initial genotype may change in function over time, giving rise to further developmental change. Environmental factors affecting development may include both diet and disease exposure, as well as social, emotional, and cognitive experiences. However, examination of environmental factors also shows that young human beings can survive within a fairly broad range of environmental experiences.
Rather than acting as independent mechanisms, genetic and environmental factors often interact to cause developmental change. Some aspects of child development are notable for their plasticity, or the extent to which the direction of development is guided by environmental factors as well as initiated by genetic factors. When an aspect of development is strongly affected by early experience, it is said to show a high degree of plasticity; when the genetic make-up is the primary cause of development, plasticity is said to be low. Plasticity may involve guidance by endogenous factors like hormones as well as by exogenous factors like infection.
One kind of environmental guidance of development has been described as experience-dependent plasticity, in which behavior is altered as a result of learning from the environment. Plasticity of this type can occur throughout the lifespan and may involve many kinds of behavior, including some emotional reactions. A second type of plasticity, experience-expectant plasticity, involves the strong effect of specific experiences during limited sensitive periods of development. For example, the coordinated use of the two eyes, and the experience of a single three-dimensional image rather than the two-dimensional images created by light in each eye, depend on experiences with vision during the second half of the first year of life. Experience-expectant plasticity works to fine-tune aspects of development that cannot proceed to optimum outcomes as a result of genetic factors working alone.
In addition to the existence of plasticity in some aspects of development, genetic-environmental correlations may function in several ways to determine the mature characteristics of the individual. Genetic-environmental correlations are circumstances in which genetic factors make certain experiences more likely to occur. For example, in passive genetic-environmental correlation, a child is likely to experience a particular environment because his or her parents' genetic make-up makes them likely to choose or create such an environment. In evocative genetic-environmental correlation, the child's genetically-caused characteristics cause other people to respond in certain ways, providing a different environment than might occur for a genetically-different child; for instance, a child with Down syndrome may be treated more protectively and less challengingly than a non-Down child. Finally, an active genetic-environmental correlation is one in which the child chooses experiences that in turn have their effect; for instance, a muscular, active child may choose after-school sports experiences that create increased athletic skills, but perhaps preclude music lessons. In all of these cases, it becomes difficult to know whether child characteristics were shaped by genetic factors, by experiences, or by a combination of the two.
Research issues and methods 
- What develops? What relevant aspects of the individual change over a period of time?
- What are the rate and speed of development?
- What are the mechanisms of development – what aspects of experience and heredity cause developmental change?
- Are there normal individual differences in the relevant developmental changes?
- Are there population differences in this aspect of development (for example, differences in the development of boys and of girls)?
Empirical research that attempts to answer these questions may follow a number of patterns. Initially, observational research in naturalistic conditions may be needed to develop a narrative describing and defining an aspect of developmental change, such as changes in reflex reactions in the first year. This type of work may be followed by correlational studies, collecting information about chronological age and some type of development such as vocabulary growth; correlational statistics can be used to state change. Such studies examine the characteristics of children at different ages. These methods may involve longitudinal studies, in which a group of children are re-examined on a number of occasions as they get older,or cross-sectional studies, in which groups of children of different ages are tested once and compared with each other, or there may be a combination of these approaches. Some child development studies examine the effects of experience or heredity by comparing characteristics of different groups of children in a necessarily non-randomized design. Other studies can use randomized designs to compare outcomes for groups of children who receive different interventions or educational treatments.
Developmental milestones 
Milestones are changes in specific physical and mental abilities (such as walking and understanding language) that mark the end of one developmental period and the beginning of another. For stage theories, milestones indicate a stage transition. Studies of the accomplishment of many developmental tasks have established typical chronological ages associated with developmental milestones. However, there is considerable variation in the achievement of milestones, even between children with developmental trajectories within the normal range. Some milestones are more variable than others; for example, receptive speech indicators do not show much variation among children with normal hearing, but expressive speech milestones can be quite variable.
A common concern in child development is developmental delay involving a delay in an age-specific ability for important developmental milestones. Prevention of and early intervention in developmental delay are significant topics in the study of child development. Developmental delays should be diagnosed by comparison with characteristic variability of a milestone, not with respect to average age at achievement. An example of a milestone would be eye-hand coordination, which includes a child's increasing ability to manipulate objects in a coordinated manner. Increased knowledge of age-specific milestones allows parents and others to keep track of appropriate development.
Aspects of child development 
Child development is not a matter of a single topic, but progresses somewhat differently for different aspects of the individual. Here are descriptions of the development of a number of physical and mental characteristics.
Physical growth 
Physical growth in stature and weight occurs over the 15–20 years following birth, as the individual changes from the average weight of 3.5 kg and length of 50 cm at full term birth to full adult size. As stature and weight increase, the individual's proportions also change, from the relatively large head and small torso and limbs of the neonate, to the adult's relatively small head and long torso and limbs.
Speed and pattern of development 
The speed of physical growth is rapid in the months after birth, then slows, so birth weight is doubled in the first four months, tripled by age 12 months, but not quadrupled until 24 months. Growth then proceeds at a slow rate until shortly before puberty (between about 9 and 15 years of age), when a period of rapid growth occurs. Growth is not uniform in rate and timing across all body parts. At birth, head size is already relatively near to that of an adult, but the lower parts of the body are much smaller than adult size. In the course of development, then, the head grows relatively little, and torso and limbs undergo a great deal of growth.
Mechanisms of developmental change 
Genetic factors play a major role in determining the growth rate, and particularly the changes in proportion characteristic of early human development. However, genetic factors can produce the maximum growth only if environmental conditions are adequate. Poor nutrition and frequent injury and disease can reduce the individual's adult stature, but the best environment cannot cause growth to a greater stature than is determined by heredity.
Individual variation versus disease 
Individual differences in height and weight during childhood are considerable. Some of these differences are due to family genetic factors, others to environmental factors, but at some points in development they may be strongly influenced by individual differences in reproductive maturation.
The American Association of Clinical Endocrinologists defines short stature as height more than 2 standard deviations below the mean for age and gender, which corresponds to the shortest 2.3% of individuals. In contrast, failure to thrive is usually defined in terms of weight, and can be evaluated either by a low weight for the child's age, or by a low rate of increase in the weight. A similar term, stunted growth, generally refers to reduced growth rate as a manifestation of malnutrition in early childhood.
Motor development 
Abilities for physical movement change through childhood from the largely reflexive (unlearned, involuntary) movement patterns of the young infant to the highly skilled voluntary movements characteristic of later childhood and adolescence.
"Motor learning refers to the increasing spatial and temporal accuracy of movements with practice". Motor skills can be divided into two categories: first as basic skills necessary for everyday life and secondly, as recreational skills such as skills for employment or certain specialties based on interest.
Speed and pattern of development 
The speed of motor development is rapid in early life, as many of the reflexes of the newborn alter or disappear within the first year, and slows later. Like physical growth, motor development shows predictable patterns of cephalocaudal (head to foot) and proximodistal (torso to extremities) development, with movements at the head and in the more central areas coming under control before those of the lower part of the body or the hands and feet. Types of movement develop in stage-like sequences; for example, locomotion at 6–8 months involves creeping on all fours, then proceeds to pulling to stand, "cruising" while holding on to an object, walking while holding an adult's hand, and finally walking independently. Older children continue the sequence by walking sideways or backward, galloping, hopping, skipping with one foot and walking with the other, and finally skipping. By middle childhood and adolescence, new motor skills are acquired by instruction or observation rather than in a predictable sequence. There are Executive Functions of the brain (working memory, timing measure of inhibition and switching) which are important to motor skills.critiques the order of Executive Functioning leads to Motor Skills, suggesting Motor Skills can support Executive Functioning in the brain.
Mechanisms of motor development 
The mechanisms involved in motor development involve some genetic components that determine the physical size of body parts at a given age, as well as aspects of muscle and bone strength. The main areas of the brain involved in motor skills are the frontal cortex, parietal cortex and basal ganglia. The dorsolateral frontal cortex is responsible for strategic processing. The parietal cortex is important in controlling perceptual-motor integration and the basal ganglia and supplementary motor cortex are responsible for motor sequences. Nutrition and exercise also determine strength and therefore the ease and accuracy with which a body part can be moved. Flexibility is also impacted by nutrition and exercise as well. It has also been shown that the frontal lobe develops posterio-anteriorally (from back to front). This is significant in motor development because the hind portion of the frontal lobe is known to control motor functions. This form of development is known as "Portional Development" and explains why motor functions develop relatively quickly during normal childhood development, while logic, which is controlled by the middle and front portions of the frontal lobe, usually will not develop until late childhood and early adolescence. Opportunities to carry out movements help establish the abilities to flex (move toward the trunk) and extend body parts, both capacities are necessary for good motor ability. Skilled voluntary movements such as passing objects from hand to hand develop as a result of practice and learning. Mastery Climate is a suggested successful learning environment for children to promote motor skills by their own motivation. This promotes participation and active learning in children, which according to Piaget's developmental theory is extremely important in early childhood rule.
Individual differences 
Normal individual differences in motor ability are common and depend in part on the child's weight and build. However, after the infant period, normal individual differences are strongly affected by opportunities to practice, observe, and be instructed on specific movements. Atypical motor development such as persistent primitive reflexes beyond 4–6 months or delayed walking may be an indication of developmental delays or problems such as autism, cerebral palsy, or down syndrome . Lower motor coordination results in difficulties with speed accuracy and trade-off in complex tasks.
Children with disabilities 
Children with Down syndrome are late to reach major motor skills milestones. A few examples of these milestones are grasping, rolling, sitting up and walking. Little is known about children with Down syndrome but commonly hypotonia or poor muscle mass is to blame. Research studies on the mental illness are old and outdated.
Population differences 
Regardless of the culture a baby is born into, they are born with a few core domains of knowledge. These principals allow him or her to make sense of their environment and learn upon previous experience by using motor skills such as grasping or crawling. There are some population differences in motor development, with girls showing some advantages in small muscle usage, including articulation of sounds with lips and tongue. Ethnic differences in reflex movements of newborn infants have been reported, suggesting that some biological factor is at work. Cultural differences may encourage learning of motor skills like using the left hand only for sanitary purposes and the right hand for all other uses, producing a population difference. Cultural factors are also seen at work in practiced voluntary movements such as the use of the foot to dribble a soccer ball or the hand to dribble a basketball.
Cognitive/intellectual development 
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What develops? 
The capacity to learn, remember, and symbolise information, and to solve problems, exists at a simple level in young infants, who can perform cognitive tasks such as discriminating animate and inanimate beings or recognizing small numbers of objects. During childhood, learning and information-processing increase in speed, memory becomes increasingly longer, and symbol use and the capacity for abstraction develop until a near-adult level is reached by adolescence.
Mechanisms of cognitive development 
Cognitive development has genetic and other biological mechanisms, as is seen in the many genetic causes of mental retardation. Environmental factors including food and nutrition, responsiveness of parents, daily experiences, physical activity and love can influence early brain development of children. However, although it is assumed that brain functions cause cognitive events, it has not been possible to measure specific brain changes and show that they cause cognitive change. Developmental advances in cognition are also related to experience and learning, and this is particularly the case for higher-level abilities like abstraction, which depend to a considerable extent on formal education.
Individual differences 
There are normal individual differences in the ages at which specific cognitive abilities are achieved, but schooling for children in industrialized countries is based on the assumption that these differences are not large. Atypical delays in cognitive development are problematic for children in cultures that demand advanced cognitive skills for work and for independent living.
Population differences 
There are few population differences in cognitive development. Boys and girls show some differences in their skills and preferences, but there is a great deal of overlap between the groups. Differences in cognitive achievement of different ethnic groups appears to result from cultural or other environmental factors.
Social-emotional development 
What develops? 
Newborn infants do not seem to experience fear or have preferences for contact with any specific people. In the first few months they only experience happiness, sadness, and anger. A baby’s first smile usually occurs between 6 and 10 weeks. It is called a ‘social smile’ because it usually occurs during social interactions. By about 8–12 months, they go through a fairly rapid change and become fearful of perceived threats; they also begin to prefer familiar people and show anxiety and distress when separated from them or approached by strangers.
Separation anxiety is a normal stage of development to an extent. Kicking, screaming, and throwing temper tantrums are perfectly normal symptoms for separation anxiety. Depending on the level of intensity, one may determine whether or not a child has separation anxiety disorder. This is when a child constantly refuses to separate from the parent, but in an intense manner. This can be given special treatment but the parent usually cannot do anything about the situation.
The capacity for empathy and the understanding of social rules begin in the preschool period and continue to develop into adulthood. Middle childhood is characterized by friendships with age-mates, and adolescence by emotions connected with sexuality and the beginnings of romantic love. Anger seems most intense during the toddler and early preschool period and during adolescence.
Speed and pattern of development 
Some aspects of social-emotional development, like empathy, develop gradually, but others, like fearfulness, seem to involve a rather sudden reorganization of the child's experience of emotion. Sexual and romantic emotions develop in connection with physical maturation.
The ability to learn temporal patterns in sequenced actions was investigated in elementary-school age children. Temporal learning depends upon a process of integrating timing patterns with action sequences. Children ages 6–13 and young adults performed a serial response time task in which a response and a timing sequence were presented repeatedly in a phase-matched manner, allowing for integrative learning. The degree of integrative learning was measured as the slowing in performance that resulted when phase-shifting the sequences. Learning was similar for the children and adults on average but increased with age for the children. Executive function measured by Wisconsin Card Sorting Test (WCST) performance as well as a measure of response speed also improved with age. Finally, WCST performance and response speed predicted temporal learning. Taken together, the results indicate that temporal learning continues to develop in pre-adolescents and that maturing executive function or processing speed may play an important role in acquiring temporal patterns in sequenced actions and the development of this ability.
Genetic factors appear to regulate some social-emotional developments that occur at predictable ages, such as fearfulness, and attachment to familiar people. Experience plays a role in determining which people are familiar, which social rules are obeyed, and how anger is expressed.
Parenting practices have been shown to predict children's emotional intelligence. The objective is to study the time mothers and children spent together in joint activity, the types of activities that they develop when they are together, and the relation that those activities have with the children's trait emotional intelligence. Data was collected for both mothers and children (N = 159) using self-report questionnaires. Correlations between time variables and trait emotional intelligence dimensions were computed using Pearson's Product-Moment Correlation Coefficient. Partial correlations between the same variables controlling for responsive parenting were also computed. The amount of time mothers spent with their children and the quality of their interactions are important in terms of children's trait emotional intelligence, not only because those times of joint activity reflect a more positive parenting, but because they are likely to promote modeling, reinforcement, shared attention, and social cooperation.
Individual differences 
Normal individual differences in motor ability are common and depend in part on the child's weight and build. However, after the infant period, normal individual differences are strongly affected by opportunities to practice, observe, and be instructed on specific movements. Atypical motor development may be an indication of developmental delays or problems such as autism or cerebral palsy.
Population differences 
Population differences may occur in older children, if, for example they have learned that it is appropriate for boys to express emotion or behave differently than girls, or if customs learned by children of one ethnic group are different from those learned in another. Social and emotional differences between boys and girls of a given age may also be associated with differences in the timing of puberty characteristic of the two sexes.
What develops? 
In addition to acquiring a large spoken vocabulary, there are four main areas in which the child must attain competence, regardless of the language or dialect spoken. These are referred to as phonology or sounds, semantics or the encoded meanings, syntax or the way in which words are combined and pragmatics or knowledge of how language is used in different contexts.
Speed and pattern of development 
Receptive language, the understanding of others' speech, has a gradual development beginning at about 6 months. However, expressive language, the production of words, moves rapidly after its beginning at about a year of age, with a "vocabulary explosion" of rapid word acquisition occurring in the middle of the second year. This vocabulary expansion is closely linked to the ability to repeat spoken words and enables the rapid acquisition of skill in their pronunciation. Grammatical rules and word combinations appear at about age two. Mastery of vocabulary and grammar continue gradually through the preschool and school years. Adolescents still have smaller vocabularies than adults and experience more difficulty with constructions like the passive voice.
Babies from one month old can produce "ooh" sounds which appear to grow out of pleasurable interactions with caregivers in a mutual "dialogue". According to Stern, this process is communication of affect between adult and infant in a mutual, rhythmic interaction. The atonement and "gaze-coupling" in which infant and adult take different roles is thought to anticipate the give-and-take of later dialogue.
From about 6 to 9 months babies produce more vowels, some consonants and echolalia, or the frequent repetition of sounds like "dadadada" which appear to have some phonetic characteristics of later speech. It is thought that a crucial part of the development of speech is the time caregivers spend "guessing" what their infants are trying to communicate thus integrating the child into their social world. When infants are trying to learn words from others they tend to create protowords, which is a "unique string of phonemes that serve word-like functions." The attribution of intentionality to the infant's utterances has been called "shared memory" and forms a complex series of actions, intentions and actions in response in an improvised way.
It has been argued that children's phonological systems develop in ways that are parallel to adult languages, even if they are using unrecognizable "words". First words have the function of naming or labeling but also condense meaning as in "milk" meaning "I want milk". Vocabulary typically grows from about 20 words at 18 months to around 200 words at 21 months. From around 18 months the child starts to combine words into two word sentences. Typically the adult expands it to clarify meaning. By 24–27 months the child is producing three or four word sentences using a logical, if not strictly correct, syntax. The theory is that children apply a basic set of rules such as adding 's' for plurals or inventing simpler words out of words too complicated to repeat like "choskit" for chocolate biscuit. Following this there is a rapid appearance of grammatical rules and ordering of sentences. There is often an interest in rhyme, and imaginative play frequently includes conversations. Children's recorded monologues give insight into the development of the process of organizing information into meaningful units.
By three years the child is beginning to use complex sentences, including relative clauses, although still perfecting various linguistic systems.  By five years of age the child's use of language is very similar to that of an adult. From the age of about three children can indicate fantasy or make-believe linguistically, produce coherent personal stories and fictional narrative with beginnings and endings. It is argued that children devise narrative as a way of understanding their own experience and as a medium for communicating their meaning to others. The ability to engage in extended discourse emerges over time from regular conversation with adults and peers.  For this the child needs to learn to combine his perspective with that of others and with outside events and learn to use linguistic indicators to show he is doing this. They also learn to adjust their language depending on to whom they are speaking. Typically by the age of about 9 a child can recount other narratives in addition to their own experiences, from the perspectives of the author, the characters in the story and their own views.
Mechanisms of language development 
Although the role of adult discourse is important in facilitating the child's learning, there is considerable disagreement amongst theorists about the extent to which children's early meanings and expressive words arises directly from adult input as opposed to intrinsic factors relating to the child's cognitive functions. Findings about the initial mapping of new words, the ability to decontextualise words and refine meaning are diverse. One hypothesis is known as the syntactic bootstrapping hypothesis, referring to the child's ability to infer meaning from cues, using grammatical information from the structure of sentences. Another is the multi-route model in which it is argued that context-bound words and referential words follow different routes; the first being mapped onto event representations and the latter onto mental representations. In this model, although parental input has a critical role, children rely on cognitive processing to establish subsequent use of words. However, naturalistic research on language development has indicated that preschoolers' vocabularies are strongly associated with the number of words addressed to them by adults.
There is as yet no single accepted theory of language acquisition. Current explanations vary in emphasis from learning theory, with its emphasis on reinforcement and imitation (Skinner), to biological, nativist theories, with innate underlying mechanisms (Chomsky and Pinker), to a more interactive approach within a social context (Piaget and Tomasello). Behaviorists argue that given the universal presence of a physical environment and, usually, a social environment, any theory of language must account for the effects of the contingent relations of these on an individuals development of language behaviour. Pinker argues that complex language is universal and has an innate basis. Pinker's argument is partly based on the development of creole languages from pidgins. The children of parents who communicate, without grammatical structures, in pidgin, develop a creole language of their own accord, complete with standardised word orders, markers for present, future and past tenses and subordinate clauses. There is some support for this from the development of sign language amongst deaf children thrown together at a young age in special schools in Nicaragua who spontaneously developed a pidgin which was then developed into a creole by a younger generation of children coming into the schools, (ISN). dogs and paws what up im here.
Individual differences 
Delays in language is the most frequent type of developmental delay. According to demographics 1 out of 5 children will learn to talk or use words later than other children their age. Speech/language delay is three to four times more common in boys than in girls. Some children will also display behavioral problems due to their frustration of not being able to express what they want or need.
Simple speech delays are usually temporary. Most cases are solved on their own or with a little extra attribution from the family. It’s the parent’s duty to encourage their baby to talk to them with gestures or sounds and for them to spend a great amount of time playing with, reading to, and communicating with their baby. In certain circumstances, parents will have to seek professional help, such as a speech therapist.
It is important to take into considerations that sometimes delays can be a warning sign of more serious conditions that could include hearing loss, developmental delay in other areas, or even an autism spectrum disorder (ASD). 
Environmental causes 
There are many environmental causes that are linked to language delays and they include situations such as, the child is having their full attention on other skills, such as walking perfectly, rather than on language. The child may have a twin or a sibling in which their age are relatively close, and may not be receiving the parent’s full attention. Another circumstance could be a child that is in a daycare that provides few adults to be able to administer individual attention. Perhaps the most obvious component would be a child that suffers from psychosocial deprivation such as poverty, malnutrition, poor housing, neglect, inadequate linguistic stimulation, or emotional stress. 
Physical causes 
Language delay can be caused by a substantial amount of underlying disorders, such as mental retardation. Mental retardation takes part for more than 50 percent of language delays. Language delay is usually more rigorous than other developmental delays in retarded children, and it is usually the first obvious symptom of mental retardation. Mental retardation accounts to global language delay, including delayed auditory comprehension and use of gestures. 
Impaired hearing is one of the most common causes of language delay. A child who can not hear speech in a clear and consistent manner will have a language delay. Even the most minimum hearing impairment can considerably affect language development. Essentially, the more the severe the impairment, the more serious the language delay. Nevertheless, deaf children that are born to families who use sign language develop infant babble and use a fully expressive sign language at the same pace as hearing children.
Dyslexia is a developmental reading disorder that occurs when the brain does not properly recognize and process certain symbols. Children with dyslexia may have encounter problems in rhyming and separating sounds that compose words. These abilities are essential in learning to read. Early reading skills rely heavily on word recognition. This involves in having the ability to separate out the sounds in words and be able to match them with letter and groups of letters. Because they have trouble in connecting sounds of language to the letter of words, this may result difficulty in understanding sentences. They have confusion in mistaking letters such as "b" and "d". For the most part, symptoms of dyslexia may include, difficulty in determining the meaning of a simple sentence, learning to recognize written words, and difficulty in rhyming.
Autism and speech delay are usually correlated. Problems with verbal language are the most common signs seen in autism.Early diagnosis and treatment of autism can significantly help the child improve their speech skills. Autism is recognized as one of the five pervasive developmental disorders, distinguished by problems with language, speech, communication and social skills that present in early childhood. Some common autistic syndromes are the following, being limited to no verbal speech, echolalia or repeating words out of context, problems responding to verbal instruction and may ignore others who speak directly.
Risk factors for poor child development 
Child development can be negatively influenced by a number of risk factors, many of which have been studied in developing countries. Malnutrition, maternal depression and maternal substance abuse are three of these factors which have received particular attention by researchers, however, many more factors have been considered.
Postnatal depression 
Although there are a large number of studies contemplating the effect of maternal depression and postnatal depression of various areas of infant development, they are yet to come to consensus regarding the true effects. There are numerous studies indicating a negative impact on development, and equally there are many proclaiming no effect of depression on development. A study of 18 month olds whose mothers suffered depressive symptoms while they were 6 weeks and/or 6 months old indicated that maternal depression had no effect on the child’s cognitive development at 18 months. Furthermore, the study indicates that maternal depression combined with a poor home environment is more likely to have an effect on cognitive development. However, the authors conclude that it may be that short term depression has no effect, where as long term depression could cause more serious problems. A further longitudinal study spanning 7 years again indicate no effect of maternal depression on cognitive development as a whole, however it found a gender difference in that boys are more susceptible to cognitive developmental issues when their mothers suffer depression. This thread is continued in a study of children up to 2 years old. The study reveals a significant difference on cognitive development between genders, with girls having a higher score, however this pattern is found regardless of the child’s mother’s history of depression. Infants with chronically depressed mothers showed significantly lower scores on the motor and mental scales within the Bayley Scales of Infant Development, contrasting with many older studies. A similar effect has been found at 11 years: male children of depressed mothers score an average of 19.4 points lower on an IQ test than those with healthy mothers, although this difference is much lower in girls. 3 month olds with depressed mothers show significantly lower scores on the Griffiths Mental Development Scale, which covers a range of developmental areas including cognitive, motor and social development. It has been suggested that interactions between depressed mothers and their children may have an impact on social and cognitive abilities in later life. Maternal depression has been shown to influence the mothers’ interaction with her child. When communicating with their child, depressed mothers fail to make changes to their vocal behaviour, and tend use unstructured vocal behaviours. Furthermore, when infants interact with depressed mothers they show signs of stress, such as increased pulse and raised cortisol levels, and make more use of avoidance behaviours, for example looking away, compared to those interacting with healthy mothers. The impact of mother-infant interaction at 2 months has been shown to affect the child’s cognitive performance at 5 years.
Maternal cocaine abuse 
Research has provided conflicting evidence regarding the impact of maternal substance abuse during and after pregnancy on children’s development. Children exposed to cocaine weigh less than those not exposed at numerous ages ranging from 6 to 30 months. Furthermore studies indicate that the head circumference of children exposed to cocaine is lower than those unexposed. On the other hand, two more recent studies found no significant differences between those exposed to cocaine and those who were not in either measure. Maternal cocaine use may also affect the child’s cognitive development, with exposed children achieving lower scores on measures of psychomotor and mental development. However, again there is conflicting evidence, and a number of studies indicate no effect of maternal cocaine use on their child’s cognitive development. Motor development can be negatively impacted by maternal cocaine abuse. As is the case for cognitive and physical development, there are also studies showing no effect of cocaine use on motor development.
Malnutrition is a large problem in developing nations, and has an important impact on young children’s weight and height. Children suffering malnutrition in Columbia weighed less than those living in upper class conditions at the age of 36 months (11.88 kg compared to 14 kg), similarly, malnourished children were shorter than well-nourished children, again at 36 months (85.3 cm in malnourished children; 94 cm in well-nourished children  Malnutrition has been indicated as a negative influence on childhood IQ. Although it is now suggested that this effect is nullified when parental IQ is considered, implying that this difference is genetic.
The impact of low iron levels on cognitive development and IQ is a subject still to reach consensus. Some evidence suggests that well-nourished children with lower levels of iron and folate (although not at such a level to be considered deficient) have a lower IQ than those with higher levels of iron and folate. Furthermore, anaemic children perform worse on cognitive measures than non-anaemic children. These nutrients have been strongly implicated in brain development, along with iodine and zinc. Iodine is required for the generation of thyroid hormones necessary for brain development. Iodine deficiency may reduce IQ by an average of 13.5 points compared to healthy individual. Zinc deficiency has also been shown to have a negative impact on childhood growth and development.
Socioeconomic status 
Socioeconomic status is measured primarily based on the factors of income, educational attainment and occupation. Current investigations into the role of socioeconomic factors on child development repeatedly show that continual poverty is more harmful on IQ, and cognitive abilities than short-lived poverty. Children in families who experience persistent financial hardships and poverty have significantly impaired cognitive abilities compared to those in families who do not face this issue. Low income poverty can cause a number of further issues shown to effect child development, such as malnutrition and lead poisoning due to lead paint found on the walls of some houses. Child blood levels of lead increase as income decreases. Income poverty is associated with a 6–13 point reduction in IQ for those earning half of the poverty threshold compared to those earning twice the poverty threshold. That being said, children coming from households featuring continual or temporary poverty still perform lower than children in middle-class families.
Parental educational attainment is the most significant socioeconomic factor in predicting the child’s cognitive abilities, those with a mother with high IQ are likely to have higher IQs themselves. Similarly, maternal occupation is associated with better cognitive achievement. Those whose mothers’ job entails problem-solving are more likely to be given stimulating tasks and games, and are likely to achieve more advanced verbal competency.
Poverty-stricken children are subjected to fewer stimulating recreational activities, often missing out on trips to libraries or museums, and are unable to access a tutor to help with problematic academic areas.
A further factor in a child’s educational attainment involves the school environment, more specifically teacher expectations and attitudes. It has been argued that teachers perceive low-SES children as being less academically able and as such provide them with less attention and reinforcement.
Diarrhoea caused by the parasitic disease Giardiasis is associated with lower IQ. Parasitic worms (helminths) are associated with nutritional deficiencies that are known to be a risk to child development. In particular, intestinal parasitism being one of the most neglected tropical diseases in the developed world. Harboring of this parasite could adverse several health implications in children affecting childhood development and morbidity. Reducing the prevalence of the parasite can be a benefit in child growth, development and educational outcome.
High levels of lead in the blood is associated with attention deficits, while arsenic poisoning has a negative effect on verbal and full IQ. Manganese poisoning due to levels in drinking water is also associated with a reduced IQ of 6.2 points between the highest and lowest level of poisoning. Prenatal exposure to various pesticides including organophosphates, and chlorpyrifos has also been linked to reduced IQ score. Organophosphates have been specifically linked to poorer working memory, verbal comprehension, perceptual reasoning and processing speed.
Other factors 
Cognitive development is related to childhood exposure to violence and trauma, including spousal abuse between the parents and sexual abuse. Intrauterine growth retardation is associated with learning deficits in childhood, and as such, is related to lower IQ.
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Further reading 
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- Child Development Guide | Developmental Stages From Birth To Teens
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