My son came home talking about heaven and hell at age 6. My husband and I are atheists also. I purchased the books Parenting Beyond Belief and Raising Freethinkers, but they were not as helpful as I thought they would be. They sort of try to explain atheism to non-atheists instead of what I thought they would do: help me teach my son how to politely disagree with the kids talking about heaven and hell.
Per my son's request, we attended a Unitarian Universalist congregation for about a year. Through them, he learned religious tolerance and that there are lots of different faiths, including non-theism. I think it was good for him, but we are so out of the organized religion loop that we couldn't continue for longer than a year. I'm guessing that when he gets a little older, we will hear more about it.
