Within the Jaranilla family, Zaijian is the eldest of three. His first few years were spent in poverty, and his parents separated when he was just 5 years of age. Currently, he lives with his father, Zenon, his grandmother, and his two younger siblings, Zildjan and Zymec.
Jaranilla is best-known for portraying Santino in May Bukas Pa, a teleserye inspired by the 1955 Spanish film, Marcelino pan y vino. Jaranilla's character vastly affects the lives of the residents of Bagong Pag-asa, as he becomes a powerful intercessor and healer known as the "Miracle Boy." Santino often directly communicated with Jesus, whom he had a casual, child-like friendship with and affectionately referred to as "Bro."