Cross reference
Mark 10:15
15 Most assuredly I tell you, whoever will not receive the Kingdom of God like a little child, he will in no way enter into it."
Matthew 18:3
3 and said, "Most assuredly I tell you, unless you turn, and become as little children, you will in no way enter into the Kingdom of Heaven.
Luke 18:17
17 Most assuredly, I tell you, whoever doesn't receive the Kingdom of God like a little child, he will in no way enter into it."
John 3:3-6
3 Jesus answered him, "Most assuredly, I tell you, unless one is born anew,{The word translated "anew" here and in John 3:7 (anothen) also means "again" and "from above".} he can't see the Kingdom of God."
4 Nicodemus said to him, "How can a man be born when he is old? Can he enter a second time into his mother's womb, and be born?"
5 Jesus answered, "Most assuredly I tell you, unless one is born of water and spirit, he can't enter into the Kingdom of God!
6 That which is born of the flesh is flesh. That which is born of the Spirit is spirit.