Sadako needs to be put into context very carefully. It can be read as an antiwar book, because innocent people are always hurt, but it takes work to make it anti-American. It can also be read as a story about courage in adversity, about friendship and about remembrance. By the time a child is 10, he has probably experienced loss. If the book is approached this way, rather than as a political comment, it's a very appropriate choice to encourage conversation and thought about the kind of loss that feels unjust and random to a child.

It was originally published in 1977, I think, certainly in the midst of the Cold War, when fear of nuclear annihilation was high and Americans had completely reaccepted the Japanese as friends. Children ought to have this information presented to them too. Those who understand what it means will understand the context better; for those who don't, they acquire an additional bit of trivia which may make an impression later.

Mercedes is really a picture book, but the vocabulary is challenging enough for older readers. A couple new books about the chocolate pilots and the Berlin Airlift have come out lately that might interest the two of you.

Ambrose's book portrays the history of WWII specifically for children: big two-page spreads on important events with lots of photographs. It's a serious history, but intended for people aged 9 and up. He doesn't pull punches depicting the war and its effects, but he is mindful of the age of his audience.

If the story that scared your son is indeed The Egypt Game, I've used that myself for children from 8 to 12 in a program we called Book Explorers. (We used the club that the characters established to explore the culture of Egypt for our enrichment activities.) It's very much about secrets and assumptions. The children keep their club a secret, and they trespass, harmlessly, to establish their secret club in a place where they think (wrongly) adult eyes can't see them. The adults know about a predator in town, but conceal the depth of the danger from the children to avoid alarming them. The children assume someone is dangerous on account of appearance. The adults assume someone is harmless on account of appearance. And this is only the subplot! The main plot is about trust and friendship among the five children themselves. So, yeah, this is a good book for grades 4 and up, too.

Anxiety sometimes manifests itself in children in ways we don't anticipate. Sometimes they become anxious about, say, a serial killer when they have recently experienced real fear that someone they love who protects them will no longer be around. What others think of as just a creepy story becomes a vector for residual fear to express itself.

If you have any concerns about what your son is reading, you have the right to insist they find alternate material to use with him. Personally, I've found that reading the book at home and talking about it there works better. He won't feel singled out in school, he'll see his parents taking an active, specific interest in his school work, and he'll not only have something serious to talk about, but time to talk to you as well.