The Boy in Striped Pajamas by John Boyne (2006)

An intense young adult book about a young boy, who is the son of the comandant at Auschwitz. He is disappointed to leave his family home and friends to move out to this house next to a fence. As he starts to explore, he meets a boy his own age on the other side of the fence, but he never really understands what is going on. Boyne manages to treat this heavy topic with great sensitivity - balancing between the boy's naievete and the horror of the reality.