What bible verse talks about leaving behind childish faith?

Answer 1

Actually, it's the other way around. Jesus tells us we need the faith of a child. Here is the verse below. Go to that chapter and read it in its entirety to understand why Jesus says what he says.

Matthew 18:3

And he said: "I tell you the truth, unless you change and become like little children, you will never enter the kingdom of heaven.

Additional thoughts:

1 Corinthians 13:8-13 tells us : when I was a babe, I used to speak as a babe, to think as a babe, to reason as a babe; but now that I have become a man, I have done away with the [traits] of a babe.

It's basically explaining that the Mosaic Law served it's purpose, to point forward to the coming Messiah, and now that he arrived (in Jesus), it was time to move along and mature. We need to keep making progress, drawing ever closer to God(Hebrews 5:11-6:3) following the NEW law 'written in our hearts'

(2 Corinthians 3:3)