What happened to Bruno and Gretel in the book the boy in the stripped PJ's?

In "The Boy in the Striped Pajamas," Bruno and Gretel's lives are drastically altered when their family moves from Berlin to a house near a concentration camp, which Bruno mistakenly perceives as a farm. Throughout the story, Gretel becomes increasingly influenced by Nazi ideology, while Bruno remains naive and curious. The tragic climax occurs when Bruno sneaks into the camp to find his friend Shmuel, leading to their heartbreaking deaths in a gas chamber. Their fate underscores the innocence lost and the horrors of the Holocaust.