Re: war stories - I just stumbled upon this exhibition, Once Upon a Wartime - Classic War Stories for Children at the Imperial War Museum in London, England. The featured books include War Horse by Michael Morpurgo, which has also recently been produced on stage and in film. The others are Carrie's War (Nina Bawden), The Machine Gunners (Robert Westall), The Silver Sword (Ian Serraillier) and Little Children (Bernard Ashley).
I'm not familiar with any of them, so I can't recommend them or comment on suitable ages. I've read other Morpurgo books and he's a fine author, but I haven't read War Horse.
Another wartime children's book (trilogy actually) is The Guests of War (The Sky is Falling, Looking at the Moon and The Lights Go On Again) by Kit Pearson, about a sister and brother who leave WWII London to stay in Canada for the duration.