You can find the quote in the 18th Chapter, and verse 3 ...of the Gospel According to Matthew.

"Verily, I say unto you, except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven." ...as words by Jesus, much has been said about these verses, and much more could be said.

But, first I want to list a few other verses.

Romans 8:14, reads, "For as many as are led by the Spirit of God, they are the sons of God."

Ephesians 3:5, reads, "Which in other ages, was not made known unto the sons of men, as it is now revealed unto His holy apostles and prophets, by the Spirit."

Philippians 2:15, reads, "That ye may be blameless and harmless, the sons of God, without rebuke, in the midst of a crooked and perverse nation, among whom ye shine as lights in the world."

I John 3:1, reads, "Behold what manner of love the Father has bestowed upon us, that we should be called the sons of God ..."