I too remember thinking about death a lot when I was about this age. I went to a Catholic school, so was told about heaven, but to be honest that scared me even more (after we die we have to sit on clouds and do nothing forever? how boring...). I used to talk to my grandmother about it, as she used to tell me lots of stories about my grandfather who had died when I was a baby. I don't know exactly how I got over it, but I did. I think it's a normal phase for children to go through.