About seven years ago my wife and I (who are childless) left our old church and set out to find the best church we could in the area. We ended up in a church that practices paedocommunion (child communion). They do not practice this because they believe that the children are saved, but because they believe that the children are members of God's Covenant People because they have been baptized, as most Presbyterians do. They often point to the Passover feast as the similar Old Testament 'sacrament' where the children ate with the whole family. What other evidence, both biblical and historical, supports this practice?
Here's what my denomination, the United Methodist Church, says about child communion:
May young children receive Communion?
Certainly. As The United Methodist Book of Worship puts it, “All who intend to lead a Christian life, together with their children, are invited to receive the bread and cup.” We remember that when some of Jesus’ disciples tried to keep children away from him he said: “Let the little children come to me; do not stop them; for it is to such as these that the kingdom of God belongs” (Mark 10:14 NRSV).
But do young children know what they are doing when they receive Communion?
Do they understand the full meaning of this holy sacrament? No, and neither do any of us. It is a wonderful mystery, and children can sense wonder and mystery. Children cannot understand the full significance of family meals, but we feed them at our family tables and at Christ’s family table. Young children experience being loved by being fed. They sense the difference between being included and excluded at a family meal. They have the faith of a child, appropriate to their stage of development, which Jesus recognized and honored. Indeed, he said to adults: “Whoever does not receive the kingdom of God as a little child will never enter it” (Mark 10:15 NRSV).
I understand that other denominations have children wait until they have a better understanding of communion. I'm sure they have good, scriptural reasons for their belief.
Here's a brief overview.
The communion of children practised in the early Church, and attested by Augustine and still practised in the Greek Church, seems to have been general as late as the reign of Pascal II. Writing in 1118, Pascal said it was sufficient to give the wine to children and the very sick, as they are not able to assimilate the bread. In their case the bread was to be dipped into the wine. Just how the change took place is unknown. Odo, bishop of Paris, 1175, forbade the communion of children. The synod of Treves, 1227, denied to them the bread, and the synod of Bordeaux, 1255, the wine as well as the bread. The greater Schoolmen do not treat the subject. The Supplement of Thomas Aquinas’ Theology says that the extreme unction and the eucharist were not administered to children because both sacraments required real devotion in the recipients.