From: Mark 10:13-16
Jesus and the Children
 And they were bringing children to Him, that He might touch them; and the disciples rebuked them.  But when Jesus saw it He was indignant, and said to them, "Let the children come to Me, do not hinder them; for to such belongs the Kingdom of God.  Truly, I say to you, whoever does not receive the Kingdom of God like a child shall not enter it."  And He took them in His arms and blessed them, laying His hands upon them.
13-16. This Gospel account has an attractive freshness and vividness about it which may be connected with St. Peter, from whom St. Mark would have taken the story. It is one of the few occasions when the Gospels tell us that Christ became angry. What provoked His anger was the disciples' intolerance: they felt that these people bringing children to Jesus were a nuisance: it meant a waste of His time; Christ had more serious things to do than be involved with little children. The disciples were well-intentioned; it was just that they were applying the wrong criteria. What Jesus had told them quite recently had not registered: "Whoever receives one such child in My name receives Me; and whoever receives Me, receives not Me but Him who sent Me" (Mark 9:37).
Our Lord also stresses that a Christian has to become like a child to enter the Kingdom of Heaven. "To be little you have to believe as children believe, to love as children love, to abandon yourself as children do..., to pray as children pray" ([St] J. Escriva, "Holy Rosary", Prologue).
Our Lord's words express simply and graphically the key doctrine of man's divine sonship: God is our Father and we are His sons and daughters, His children; the whole of religion is summed up in the relationship of a son with His good Father. This awareness of God as Father involves a sense of dependence on our Father in Heaven and trusting abandonment to His loving providence--in the way a child trusts its father or mother; the humility of recognizing that we can do nothing by ourselves; simplicity and sincerity, which make us straightforward and honest in our dealings with God and man.
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.