Deuteronomy 6, the words of Moses: “You shall love the Lord your God with all your heart and with all your soul and with all your might. And these words that I command you today shall be on your heart. You shall teach them diligently to your children, and shall talk of them when you sit in your house, and when you walk by the way, and when you lie down, and when you rise. You shall bind them as a sign on your hand, and they shall be as frontlets between your eyes. You shall write them on the doorposts of your house and on your gates.”
Proverbs 22:6, “Train up a child in the way he should go, and when he is old he will not depart from it.”
And a warning from Jesus in Matthew 18, “Whoever receives one such child in My name receives Me, but whoever causes one of these little ones who believe in Me to sin, it would be better for him to have a great millstone fastened around his neck and to be drowned in the depths of the sea.”