The Boy in the Striped Pajamas?

The motto is 'A timeless story of innocence lost and humanity found.' Does Bruno ever even lose his innocence? When he's being led into a gas chamber at the end, he thinks they're just bringing them out of the rain. Is his innocence lost when he doesn't protect his friend from Lt. Kotler? I don't really think so. Is it referring to Bruno's father instead? Maybe innocence meaning guiltless, not without experience and understanding. Maybe Bruno's father feels guilty for what he's done after he figures out that Bruno got under the fence, and he finds his humanity again. Please just tell me your opinion.