Daftpunk, what happens is you teach about religions. You learn about the belief system, how it was developed, how it fits into history and how it links up with other belief systems.
It could be argued that this is a far better way of teaching our children about religion because there is not discussion about who is right (us) and who is wrong (them). If you invest in a belief system, you must, by definition, consider all other belief systems to be wrong in some way. Hence the problem of having children whose belief system is different that the school one included in a school. Imagine all those Muslim children in a Catholic school being told sublty (and not so sublty, I went to a Catholic school, I remember) that they are, of course, allowed to believe what ever thy like, but the only path to eternal life is through Jesus.
Surely it is far better to teach our children "this is what Catholics believe, this is what Muslims believe, this is what Jews believe, this is how Islam and Christianity have their roots in Judaeism" etc. No one is right, no one is wrong, no one is expected to buy into one of the belief systems in order to understand it. Everyone is included.