I don't think you should teach a religion to anyone you consider a child, because lets face it a child tends to believe whatever you tell them. And if you force a child to believe in a religion then that takes away from there ability to choose to believe in it. And in the case of at least christianity it is important to choose to do the good thing, not simply to do the good thing because you were told to. It is important to actually understand what is good and what is bad not to simply believe it because you think it will benefit you to believe it. And in the case of the child, the child tends to do whatever it thinks will benefit it the most which it generally thinks is what it is told to do.

Likewise if you say make it law to believe, then people tend to only say they believe it, thus makeing it law actually has a tendancy to make the religion less effective.