Hi michael. i don't have a child but i think if ever in the future i decided to have one. I will teach him about science and stuff. answer his questions logically and never lie. and if he gives me the big question "is God exist?" well i would answer him. not directly answer the question but another questions that would make him think and I'll give him facts about religion and why they are non-believers. teach him about science. correct the misconception about the world. why is important to be good. without expecting any reward from anyone or having a fear of punishment. That's what i think i would say. teach him what you know but not forcing what you believe in. i wouldn't be bias i would teach him about different religion and why people believe on it and how its feels good to believe on god. mostly my answer would be series of questions for him. It's helps to teach him how to think and not what to think. I will even let him attend church mass and interact with theist but not the aged of 2. I let him attend when he already knows how to think. I think it would help him learn more about the world if he interact with theist like how we learn and become atheist. be patient with your child learning. Whatever he become accept him. I know it's a pressure for a child to what to believe in especially when his parents has completely different belief. But i think your doing a good job. :) your child will grow up a better man because you are his guidance :) I hope you like my suggestions. That is just how i would do if i was in your situation but we always have different parenting style.
I think your intuition is correct in teaching him about all different sorts of religions. Also I know I've seen some pretty cool books about science and critical thinking for kids available through Skeptic magazine ( http://shop.skeptic.com/merchant.mvc?Screen=CTGY&Store_Code=SS&... ) and it's never too early to get kids interested in books!