If they do teach Christianity from a believers perspective, well let them.
Lets take this hypohesis: Say I was a teacher of your children, and happened to be a fire-worshipper. I believed "fire" was God, and provided I gave your children a good education, would you be happy for me to preach this belief to your kids?
I hope schools are there to teach facts, and not impose a group of individuals supernatural worldview on the young & innocent?
Funny how you came up with "fire worshipper"- Zoroastrians are fire worshippers, and although my father doesn't really believe that fire is God (from what I know) he feels that I should remain a fire worshipper, marry another fire worshipper and make fire worshipper kids to keep up Zoroastrian numbers. My maternal grandfather of course has tried to talk me and my brother into worshipping Allah, and regard the Koran as God's word.
I do agree that in an ideal world schools are strictly for teaching facts,indocrination of children into supernatural beliefs should be left to the parents and guardians.Maybe even some restrictions should be put on that. Sadly, sometimes religious schools happen to be the only ones around, or the best one around. The Catholic Schools worldwide produce some of the best results. I don't think that there should be state funding for faith schools, state funding should be only for all tolerant, all inclusive non denominational ones but if there was a really fantastic religious school which gave my hypothetical kids great education, taught them scientific facts and at least a moderate amount of respect for all faiths and different worldviews, I'd grudgingly tolerate the teaching of superstitious stuff.
So yes if you were a fire worshipping teacher who manages to teach my kids splendidly, I'd tolerate your idiosyncracies, and actively tell them at home that your particular belief about God has no basis in fact. Of course, I'd still search for an equally good teacher who strictly teaches facts.
Since faith schools often get such good results, and since quite a few aren't particularly fanatic ones, I'm not sure we'd be able to replace them all with equally good secular schools after we banned them.