What, if anything, do you tell your kids about God and/or religion?

DH and I were both raised going to church, but we are both somewhat skeptical and don't really make religion a part of our lives. E is 4 and has little to no understanding of God and religion. We had to put our dog down this summer and several people told him she went to heaven... He completely misunderstood and now thinks she lives with someone named Kevin

I was relaying that story to my Mom and she was disappointed that we haven't made an effort to talk to him about God and the whole shebang. We have several family members that are quite religious and the topic will come up fairly often, so it's probably good that the kids have some working knowledge of the subject... I'm just at a loss on where to even begin when it's not an idea I necessarily subscribe to. Any tips?