When Bruno and Shmuel think up their great adventure - Bruno enter the area behind the fence and the two boys would explore the area - it seems clear that something extraordinary, whether good or bad, would happen. Since Bruno still does not know that the area fascinating him is a concentration camp, he is not aware of the dangers. Neither Bruno nor Shmuel can guess what had happened to Shmuel's father who had suddenly disappeared forever.
If Bruno had known about what his father's job was about and what a concentration camp was, the ending might have been different - but the story not as touching and meaningful. The two boys, born on the same day, thus being "nearly" twins, share the same destiny from the day they meet on. Being born on the same day in the same year carries huge symbolic meaning and kind of foreshadows that their lives - and passing aways - are linked together. Yet, since they are just innocent children, the end also points out cruel and unreflected the "nazi" ideology was.
The narrator finally concludes: "Of course all this happened a long time ago and nothing like that could ever happen again. Not in this day and age." It's a wish and a hope. Yet, it is necessary to not forget what had happened so that nothing like this would ever happen again. This also means that we need people who know more about the ideology behind the events as well as about prejudices and xenophobia in general.
And one should never forget that in other parts of the Earth, further cruel human rights abuse still exists.
After reading the book, I am also thinking about watching the movie soon.