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. (Mark 10:14-16)
And calling to him a child, he put him in the midst of them, and said, “Truly, I say to you, unless you turn and become like children, you will never enter the kingdom of heaven.” (Matthew 18:2)
St Cyril of Alexandria comments on what Christ means when He tells adults that they must become like children to enter the Kingdom of God:
It is necessary, however, to examine what is the meaning of being babes in wickedness, and how a man becomes so, while in mind a grown man.
A babe then, as knowing either very little or nothing at all, is justly acquitted of the charge of depravity and wickedness; and so it is also our duty to endeavor to be like them in the very same way, by putting habits of wickedness entirely away from us, so we too may be regarded as men who do not even know the pathway leading to guile, but who, unconscious of malice and fraud, live in a simple and innocent manner, practicing gentleness and a priceless humility, and readily forbearing from wrath and spitefulness. For such we affirm are the qualities found in those who are still babes. (Commentary on the Gospel of St. Luke)
Fraternized 