Many of the commandments of the Law have to do with worship and ceremonies. As a child, Jesus accompanied his parents and their relatives to religious feasts in Jerusalem. Since the period of the Enlightenment and the Protestant Reformation, much of Christianity has taken on a more didactic than celebrative character. It is assumed that converts, including children, must be carefully taught their way into the faith, learning the truths of the Bible so that they can understand the story of Jesus and respond to him. This has often resulted in the segregation of children into age groupings for more effective teaching, separating them from the arena of adult worship.
Teaching is, of course, important.
But children learn best by imitation. Unless they are where adults are worshiping, they will miss the opportunity to learn by example. Indeed, they may decide that the worship of God is an adult activity which has no relevance for them. When we bring our children along with us into the worship life of the church, we are giving them the opportunity to act out the truths they learn in Sunday school and make them real. Not only so, but participation in worship with the whole church helps to instill in them an identity as members of the body of Christ.