Natalie's teacher also recommended Lifetimes (subtitled, "The beautiful way to explain death to children"). It focuses on the message that everything in nature is part of a cycle. By the way, if you're looking for a book about reincarnation, The Mountains of Tibet is a beautiful one.
I hope these recommendations are helpful to someone!
I have added quite a lot to my brainstorming about summer camps; I'm really looking forward to them. I'm also going to be giving some presentations at our local library about the wonderful age of 2 -- instead of the social stigma of the "terrible twos" -- so I'll post some thoughts about that and recommended books as I draft it.