Strawberry it's not children that are saying that, it is an adult who has been told in essence I do not want her teaching my son about her religion in this manner, and rather than her having some respect, she persists. How tolerant is she being?
The children at school, from what I have been told, have usually come out of religion class and talk about what they have been taught, they collectively go oh, huh, right, I was told this, they drop it and go play football. No issue there actually now his put it in context. For as much as he 'should' be asking the other children why they think that, the same goes for them don't you think?
I would never dream on continuing to bring up a subject, for example, telling a religious person that they are wrong or it's OK they believe and ignore the truth. That is being respectful.
My SMIL is very religious, she says things a lot, she posts on Facebook a lot, and I just scroll past, or gloss over it, I would never go up to her and say you know this is all rubbish, but it's OK I know whats right and wrong and I'll look after you. Or for example my cousins children who are being raised Christian, I wouldn't take them to one side, away from their parents, and tell them it's OK their being taught wrong and I'll look after them.
I'm sorry, but I think that some people of faith simply do not understand what it is to be respectful. What people do in their own homes or otherwise nothing to do with me is fine, but when they insist on dragging others (who have been clear) into it, that's not on.
Oddly enough I studied classical civilization at college, and have frequently spoken to my children about the stories, the temples, myths etc, this mostly came about after they asked about Thor.