My DS4 has been asking deep questions about death for a year at least. My parents' cats died, then our dog died. He put together that garbage decomposes and if we bury people when they die do they decompose? This freaks him out to no end.
Anyway, do typical kids not understand death as permanent at 3? Is it the depth of questioning that makes our kids' understanding of death atypical or the fact that they can't stop thinking about it? It has led to much debate on his end over if he wants to be a vegetarian, which I believe I read a discussion about here as well.