The other day he told me, "Mom, my god can fly."
"Wow, Tristan, that's cool. Is this your personal god, or is it everyone's god?"
"Anyone who wants to believe in him can I guess."
"Do you think this god is real, or is he someone you made up, like a pretend friend?"
"He's kind of a pretend friend. I don't know. I don't think he's real, but I thought him up so I could believe in god like James at school."
"Do a lot of kids talk about god at school?"
"Some people do. People at my school. James asked me and I said I don't know and he made a face like I was crazy."
"Do you think James knows for sure that there is a god?"
"No, I think he pretends like I do. I think pretend friends help you not feel lonely sometimes."
So, I feel like he's doing fine in his development in regard to god and religion in general. He's kind of interested, but at the same time he realizes that just because someone else believes something, that doesn't mean it is actually real or that he has to believe it.
One of the things I do make sure my son is exposed to is lots and lots of science. My son responds to anything in song form, so I've taken up watching They Might Be Giant podcasts and videos from their Here Comes Science CD/DVD. I can't recommend these guys enough. They're even scientifically responsible enough to have made a song which corrected an older song they released regarding why the sun shines. Now that's pretty awesome!