Consisting of the child Jesus, his mother, Mary, and his foster father, Joseph, the Holy Family has long been a subject of popular devotion. The Holy Family has given its name to a confraternity and other associations and to several religious congregations. In many places, the month of March is dedicated to its honor. Pope Leo XIII in 1893 instituted the Feast of the Holy Family, which is observed on the Sunday within the octave of the Epiphany, and it was extended to the whole Western Church in 1921 by Pope Benedict XV. The artistic custom of portraying the Holy Family with Jesus as a baby or a child is based on the belief that St. Joseph died while Jesus was young.
(From Butler’s Lives of the Saints)