The Sacrament of First Communion
According the Catholic Encyclopedia, infant communion was not uncommon throughout the Christian Church in the first centuries. However infant reception of the Eucharist was much more universal in the East, even then. It was not the general standard in the West, though the Eucharist was received by infants and very young children at certain times, especially at baptism or when severely ill and in danger of death. The current practice in the Roman Rite – that children receive First Communion upon reaching the age of reason – was established at the beginning of the 13th century, at the time of the Fourth Lateran Council.
The Catholic Encyclopedia explains that this is not a fixed age in number of years, “but rather the arrival at a certain stage in mental development, when children become able to discern the Eucharistic from ordinary bread, to realize in some measure the dignity and excellence of the Sacrament of the Altar, to believe in the Real Presence, and adore Christ under the sacramental veils.”