When I was a child, I spake as a child, I understood as a child, I thought as a child: but when I became a man, I put away childish things.
1 Corinthians 13:11

Train up a child in the way he should go: and when he is old, he will not depart from it.
Proverbs 22:6

Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven.
Matthew 18:3