I wanted to add that yes, the bombing of Pearl Harbor was "tricky" but that I would make sure he understood that didn't mean that all Japanese people were tricky and that most nations have employed "trickiness" in times of war. If he is interested it might make sense to talk about what you feel are just/unjust reasons to go to war. Re: photos--personally I would do my best to keep my child from seeing images that would be very difficult to forget. I feel differently about words. Oh, and I would probably talk about the reasons that a similar attack would not happen today if I thought that was something my child would worry about.
