The two main characters are the boys Bruno and Shmuel. Bruno is the son of a Nazi official who has been relocated to Auschwitz, which Bruno ironically calls "Out-With." Bruno is an intelligent, sensitive boy who is an analytical, thinking person with a strong moral sense. This sounds unusual for a boy, but may be less unusual than some have come to believe. Bruno's character is well illustrated when he objects to and becomes defensively protective after the way in which Lieutenant Kotler treats Pavel:
Kotler spoke to [Pavel] insolently, despite the fact that [Kotler] was young enough to be his grandson. ... "And afterwards, ... make sure you wash your hands ... you filthy__." Lieutenant Kotler repeated the word he had used twice already ....
Shmuel's character is more subtly drawn as he is seen in much limited circumstances: he is a prisoner in Auschwitz, hungry, heartsick and lonely, and has fewer interactions than Bruno has. A good illustration of Shmuel's character is his patient rendition of his story to an uncomprehending Bruno who periodically muttered under his breath the corrections he thought must be applicable to Shmuel's story:
"I think I'd quite like [an armband]. I don't know which I'd prefer though, your one or Father's."
Shmuel shook his head and continued ...
"There weren't any doors [on the train]" insisted Shmuel. "If there had been, we would have gotten off."
Bruno mumbled something under his breath along the lines of "Of course there were," but he didn't say it very loud so Shmuel didn't hear.
We know that Shmuel is very much like Bruno in kindness, good manners, conversation and intellect. He is also patient and forgiving as shaking his head at Bruno's innocence indicates. All in all, the two boys are very much like each other with one evident difference: Bruno has yet to learn fearful submission while Shmuel has already taken on the hesitancy of the oppressed, having lost his daily life, his home, his watch and--worst of all--his mother and his father.
A brief summary of each character would be when you write a description of the characters feeling, emotions, conflicts or actions. This would be things that deal in Direct Characterization and Indirect Characterzation for that character. Direct is what you are being told, and indrect being the actions or what you are shown about the character and have to realize on your own.