How does the writer John Boyne present the innocence of children amid a cruel and unpredictable world?

John Boyne's The Boy in the Striped Pajamas tells the story of Bruno and Shmuel, unlikely friends amidst the Nazi occupation in World War II. While the adults around them are living daily in the dynamic of prisoner and warden, Bruno and Shmuel carry on an innocent friendship wherein they spend time together with little regard for the fact that they live on opposite sides of the fence around a concentration camp.
Bruno does not understand the camp his father guards, and he sees Shmuel not as a prisoner but as a child allowed to play outside in his pajamas. He is so out of touch with what his father does for a living that he does not even pronounce Auschwitz correctly. Instead, he calls the camp "Out-With." The book ends with Bruno joining Shmuel in the camp, sneaking in with clothes Shmuel brings him. He thinks the camp is a fun place to spend the day and does not understand that the prisoners inside are not allowed to leave.
In addition to the facts that Boyne shares about Bruno and the little details that paint him as an innocent child, the point of view of the book also sells the fact that the children are innocent. The story is told from Bruno's perspective, and so with each twist and turn, the reader sees how Bruno interprets the world around him and how that likely differs from reality. The terrible atrocities are seen through a child's eyes until his untimely death. The moments after Bruno begins to march into the gas chamber, when the reader knows what will happen and he does not, are heart-wrenching and hammer home the fact that (Nazi) adults have bastardized the world so heartily that a child who lives within it can't imagine the danger into which he's stepping.