Kids should only learn about religions in school that their parents say are okay for them to learn. I don't want my son to learn about religions that I don't want him to be exposed to yet. Obviously few parents will want their kids to learn about witchcraft in their science class (just an example). I know that when my son is an adult he will have the sense to reject any of witchcraft's theories. But kids are impressionable. Teach the kids more about the religions that their parents have exposed them to. The best way to do this would be to seperate the kids into different classes based on what their parents want them to learn.
I'm not a religous zealot, I don't think religion should be taught in the science class (but creation science should). Of course religion would only be taught in literature, philosophy, art, and music, since religion basically creationed those subjects. You can't teach art without the Sistine Chapel.