When my older boy was 7 (I think that is right), I talked to him about the earthquake in Haiti, since it was on the news alot. Then the teacher had a special conference with us b/c he was expressing dark thoughts about how what if the school collapsed on everyone and they all died?
I don't do that anymore. I think many gifted children are very emotionally sensitive, and I just will wait until they are older to bring up mature topics like that.