The Storm to Come by Yankev Glatshteyn
As the Holocaust begins to unfold from a brutal plan into a nightmare reality, two nine-year-old boys, one German, one Jewish, find themselves living in a hell-on-earth where children come home from school to find their parents gone, where sometimes school isn't even safe, and no one, but no one can be trusted. Originally written in 1940, this book chillingly anticipates the terror of the storm to come.