I feel it is inappropriate to express any truth in religion in schools. It's a hard line but if we can agree religion is simply not based in any reality at all, why would you support its teaching or being said to be true?
People believe the moon landing was fake but we don't teach it to kids in science class.
As far as the teachers go, i would talk to the principal about any concerns you have.
And as a parent of a 6 year old, I can attest to the fact that they believe most things told to them by their teachers or trusted adults, as you would expect them to. They are spending all day teaching them to read and write and other "facts", why should anything else they tell them be false?
My son believes everything his best friend tells him. He's 6!! LOL
I want my kids to think for themselves, so I always ask them what they think before answering a question. I want them to use their critical thinking skills, but at this age, they are too impressionable. My son doesn't question Santa or the Tooth Fairy, so why should he question God existence?