Then by Morris Gleitzman 198 pages

This is a sequel to Once about two young people in Poland trying to survive the Holocaust. Felix is ten and Jewish; Zelda is younger and Catholic. They escape from a cattle car bound for a concentration camp. Felix finds Zelda a difficult companion. She hates her parents, who were Nazis and has a quick temper that attracts attention. But she has adopted him, even though she could probably survive without him since she has proof that she is not Jewish. They find respite with a gruff farmer. Felix attracts the wrath of the local young  bully as well as a survivor from a recent slaughter of Jewish orphans. As you can surmise, this is not an easy read and the ending is harsh.Poignant and memorable.