This continues to be an ongoing topic for us. DS was 3 perhaps, and cried great volumes over Little Red Riding Hood. At 4, he became a vegetarian for awhile after we walked through a fish market. Luckily I found some food chain books, and his magic schoolbus book specifically dealt with the issue- that humans are made to survive this way.
What seems to have worked also is talking about how different cultures come to terms with death. He is stubbornly atheist after attending a church kindy for awhile, but even so, he saw that different people had different ways of remembering their loved ones and coping with loss.
It doesn't resolve the long term however- we are very close and he has said he doesn't want to live after i move on, like he's sure it'll be the same viceversa. Not sure what to do about this one ...
