I have a 7 year old. We talk about religion sometimes and the afterlife a lot too since my dad died. My son was told by a lot of people that his grandpa was in heaven and it was a difficult thing to deal with. Who wants to tell their kid that heaven most likely isn't real? That the promise of seeing your grandpa again probably isn't going to happen? Sucked, but I when he asked me about it I told him what I thought, what Christians believe (since that was the story he was getting from others) and then I went over what some other cultures believed as well. I told him he could believe or not believe anything he wanted, but that if he wanted to talk to me about god and religion, he needed to understand that my position on the whole thing was that it wasn't real and that I would challenge him on anything I didn't agree with. He's taken me up on that a few times and it's been interesting. I also make sure he knowns that there's no reason why he needs to even have any beliefs if he's not totally sure of them and that even if he's sure of something, he should question it because things that are true can handle being questioned and things that are false tend to fall apart under questioning.
At this point he seems to switch from being religious to not religious almost daily. I just kind of go with it, always asking him questions.
If he asked me to take him to church I would, but I'm secretly dreading that day. Church sucked for me as a kid because I just kind of went without getting it drilled into me that religion was true, so it was just long and boring and smelled weird. Also, I myself was raised atheist so going to church, praying, all of that has always been alien to me. Even having been exposed to it quite a bit as a kid, it always made me a little uncomfortable. But, for the boy, that's a small price to pay to help him become a well rounded person.
I also make sure he knows that he doesn't have to believe the same thing as me, and that his belief or non belief isn't a point of pride/embarrassment to me. It's a personal belief he needs to consider on his own - but that I'll always be there to answer any questions he might have.