Book: Lily's Crossing by Patricia Reilly Giff (1998 Newbery Honor)
Lily is looking forward to a wonderful summer at Rockaway Beach, just like she does every summer. But things don't go as planned. First, her friend there has to move away because of her dad's war assignment. Then Lily's own dad gets a war assignment and sails away to no one knows where and she is left with only her grandmother who makes her practice the piano. Finally, a new boy moves in down the street who can't talk English too well and besides that, he's very sad and seems to have some sort of secret.
This is a great story on how WWII affected even the youngest of people, and how even though they didn't understand all that was going on, they understood enough. I think it's a perfect introduction to the stresses of the war for younger readers.
...and that's all I could find this time! Let me know if I missed yours.