If Christians had to teach God to their children themselves; they would have to start living as they preach because their children would be watching. If the school is doing the teaching; then mom & dad can just say the school taught it wrong when their children call them out on their inconsistencies with God, but if they are teaching their children themselves, and their children call them out on their inconsistency's; there is no avoiding their own hypocrisy.
Reading, writing, arithmetic, science, art, social studies, biology, phys-ed, and how to handle finances, these are things to be taught in school; God is learned at home from observing and interacting with parents.
God as the religious call it, gave them children, and commanded them to teach, train, and raise them up in the ways of their God. If God had intended Caesar to do it; God would have given those children to Caesar instead of them.
God’s instruction right out of the pages of the Christian Bible:
Proverbs 22:6 Train up a child in the way he should go, even when he is old he will not depart from it. New American Standard Bible
Ephesians 6:4 Fathers, do not provoke your children to anger; instead, bring them up in the discipline and instruction of the Lord.
Deuteronomy 4:9 "Only give heed to yourself and keep your soul diligently, so that you do not forget the things which your eyes have seen and they do not depart from your heart all the days of your life; but make them known to your sons and your grandsons.
Deuteronomy 11:19 "You shall teach them to your sons, talking of them when you sit in your house and when you walk along the road and when you lie down and when you rise up.
Nowhere in these verses from your own holy book does it even imply that you should expect, or demand that you be able to send your children to Caesar to be instructed in God. This is your responsibility, commanded to you (not Caesar) by your God.
The instruction is very clear, right from their own holy book. Religious instruction is to be accomplished at home. Not in school, in public spaces, on coins or bills, not by Caesar; but by Mom & Dad in the privacy of home.