Christian parents must teach their children to pray before eating school lunch, snack, etc as well as when they are at home. There is often a period in which children can read whatever they want. They should bring a Bible.
It is not the public school system's job to teach them the Bible and prayer. The teaching of Jesus to children must come from home primarily. Also, if parents send their children to religious meetings instead of teaching and setting the example for them at home, they are not living up to the responsibility that God placed on them.
Deuteronomy 6:5-7
You must love Jehovah your God with all your heart and all your soul and all your strength. 6 These words that I am commanding you today must be on your heart, 7 and you must inculcate them in your sons and speak of them when you sit in your house and when you walk on the road and when you lie down and when you get up.
Proverbs 22:6
6 Train a boy in the way he should go;
Even when he grows old he will not depart from it.
Ephesians 6:4
4 And fathers, do not be irritating your children, but go on bringing them up in the discipline and admonition of Jehovah.