I am at the BookExpo America looking at books available for children on World War II now that D-Day is a week away. There are surprisingly few, alhough Goodreads has 171 such books listed. Many of these books are multiple titles of the same basic text, such as Anne Frank's Diaries, which always rank near the top on this list, deservedly so. Right now it ranks #3.
Among the top 15 books are two by Hilda van Stockum. The Winged Watchman is one. It is about a family that lives in a windmill, and is deeply involved in the Resistance to the Nazi occupation. The heroes are two boys in the family, young teens. A local Dutch boy goes over to the Nazis and becomes a Landwatcher, meaning a traitor. The job of the two boys is to keep track of the traitor, Leendert.
The book is based on true stories. The author (disclosure: my mother) is Dutch-born and many of her relatives were in the Resistance.