The Boy in the Striped Pyjamas
The Boy in the Striped Pyjamas is a novel written by John Boyne. Bruno's father is a soldier in World War II and the family moves house so he can work closer to concentration camps. Bruno makes friends with a Jewish boy named Shmuel in the camp. They meet up on their side of the fence each day. One day, he accidentally enters a gas chamber while attempting to look for Shmuel's father and dies by the side of the Jewish boy.
There is a movie of the same name based on it.