An Infancy Gospel refers to any non-canonical gospel which contains information on the childhood of Jesus. The life of Jesus before his baptism is of great interest to some theologians, as the Bible is noticeably silent on Jesus' childhood. Of the four gospels in the New Testament, only two tell the story of Jesus' birth (Matthew and Luke) and only one contains any information on Jesus as a child following his birth (Luke contains a story of Jesus teaching in the Temple in Jerusalem when he was twelve years old). Aside from the birth and Temple stories, there are no references to what Jesus did as a child or a teenager within the Bible. Mark and John both start chronicling Jesus from the time of his baptism by John the Baptist, Luke 3:1 states John began his baptizing "in the fifteenth year of the reign of Tiberius Caesar" which would place Jesus at around 30 years old at the time of his baptism.

The most well known Infancy Gospel is the Infancy Gospel of Thomas, written no later than the second century AD. It tells of Jesus' late childhood, early adolescence, and his education throughout. The gospel depicts Jesus' behaviour in a way much different than the New Testament, the Infancy Gospel of Thomas portrays him as a menace. Imagine a rebellious child with god-like powers: He kills his classmates and plagues his teachers by cursing them. Joseph is told by the townspeople to send him away or to train him to control his supernatural abilities.

Despite the Infancy Gospel of Thomas having non-canonical status in Christian churches, it appears to still have some religious influence. There is a popular theory some of the stories of Jesus in the Qur'an were inspired by the Infancy Gospel of Thomas, namely, the miracle of Jesus creating a clay bird and transforming it into a real one is told both in the Infancy Gospel and in the Qur'an. 

Sources

Aasgaard, Reidar. The Childhood of Jesus: Decoding the Apocryphal Infancy Gospel of Thomas. James Clarke & Co., 2014.

Botoi, Oliviu. “The Qur'anic Image of ‘The Table Descended from Heaven’ - An Apocryphal Reproduction of the Biblical Eucharist.” Academia.edu,.

James, M.R. The Apocryphal New Testament: Being the Apocryphal Gospels, Acts, Epistles, and Apocalypses, with Other Narratives and Fragments. Clarendon Press, 1924.