In biology and sociology, alloparenting is a system of parenting in which individuals other than the actual parents act in a parental role.
One common form of alloparenting is a situation in which grandparents adopt a parental role. This is sometimes named a "skipped generation household". In 1997, 8% of children in the United States lived with their grandparents, with the grandparents being the caregivers in one third of those cases.
According to Deihl, the Efé people of Ituri Forest in the Democratic Republic of Congo practice alloparenting, with care for infants coming from siblings, grandparents, and older members of the community. Deihl states that where siblings are alloparents this provides adolescents experience of being a parent, and that similar practice in the United States would reduce the rate of teenage pregnancy and make teenage parents "better parent[s] when they do become parents".
In biology, "Cooperatively breeding vertebrate systems are characterized by individual ‘helpers’ that take care of young ones within the social group that are not their own offspring — a behaviour termed ‘alloparental care’. In mammals, care typically encompasses allolactation, pup-feeding, babysitting and carrying young." An example of this in nature is when male Barbary macaques carry around unrelated infants and care for them for hours at a time.  Another example is when warthog sows suckle piglets from other litters after the sows have lost their own litters. In some fishes such as redlip blennies, males also perform alloparental care.
^Briga, M.; Pen, I.; Wright, J. (2012). "Care for kin: Within-group relatedness and allomaternal care are positively correlated and conserved throughout the mammalian phylogeny". Biology Letters8 (4): 533–536. doi:10.1098/rsbl.2012.0159. PMC3391475. PMID22496080.edit