The narrator, a 9 year old boy named Bruno, is the son of an Nazti Commandant and the novel is written in Bruno's childish verncular. Most notably, he mishears and doesn't understand several of the important references that surround his life and the Holocaust he is living through. For example, when Adolf Hitler visits his father, Bruno hears him called "The Fury" rather than "the Führer". Also, he misunderstands Auschwitz and calls this infamous concentration camp "Out-With". These misunderstandings help add to the innocent tone of the novel.
Also, the novel includes several nicknames for characters which help add to the tone of the characterization. In the example where he calls Hitler the Fury, Bruno probably does have an idea of the negative connotation of the word "fury" so, though he doesn't understand who this man is, he does understand the negative connotation. Also, Brono's parents call his sister a "hopeless case". From the flippant way it rolls off his tongue he probably does not understand what the colloquial meaning of these words specifically but he DOES recognize the misbehavior of his sister and can imply the negative connotation.
Though Bruno does not understand the exact meaning of the things going on around him, he does interpret the negative, frightening feelings surrounding much of his life. This makes the ending of the novel even more startling and ironic because his young powers of perception failed him when it came to the atrocities that were occurring right next door to his home.