Absolutely need to be aware of the various 'main' religions they will come across, but should only be taught such things in an entirely neutral manner and environment. They should not cover all aspects of various doctrine but should be aware of the primary thoughts and ideologies of the religions as well as their histories and origins, primary figures, etc... Parents should not be allowed to remove their children from open RE classes regardless of their own religion. Also, RE teachers should not just be English/Maths/History teachers dragged from their respective departments for one class a week, as I've seen in a couple of schools.
I'm atheist. Whilst RE was compulsory in my school I still feel as though I'm lacking awareness on various religions despite my own research, and this leads to embarrassing ignorance when I come across them in real life. I think a little more could have been and can be done to present the unbiased facts of more elements of religion to children.
I do think that too many schools have embedded Christianity which needs to be addressed... we would always sing hymns, towards the end of the month we were drowned with religious Christmas stories, etc. Some of it is fine, but the way it was all worked in so easily to my early school years is a little creepy.