I'm sorry for your loss
That's pretty fucked up Girl Gun, I've never had anything like that happen to me before. I've only ever lost one person though.
As for your son, I don't know what I would tell him. I wasn't raised with any kind of religion either, but I've never been really fearful of death. I guess I would just tell him that he's not going to die for a long time, so there's no need to worry. How a kid would take that (if he took it at all) I'm not sure.