Herr Liszt is the tutor hired by Bruno's father. He basically gives the lessons in Nazi rhetoric. He goes through all the great stuff the Nazi's were doing! Ethnic cleansing, anti-Semitism, German superiority and the swell guy named Hitler were just some topics on his course outline. Yes he was taking advantage of the children. Bruno and Gretel were a captive audience and impressionable Gretel took to the lessons while Bruno was skeptical.
Grandmother tries to talk to her son (Bruno's father), but he will not listen, so she refuses to speak to him until he is willing to listen and walks out of his promotion party because she cannot stand to see him in his new commandment uniform after his promotion. This never happens before she dies, so she died with a quarrel unlamented, and her son now has to live with the thought of what he did to her.
I might consider the moment when Bruno changes his clothes and hops the fence into the death camp. Bruno has ceased to be in a state of otherness compared to Shmuel. He has disobeyed his father's instructions of, "Out Of Bounds At All No Times And No Exceptions." He has also left the safe world of the German elite and entered Shmuel's world of oppressed Jew.
Bruno is sheltered by his family. He lives in the midst of a death camp, but his mother and father keep him innocent of what happens on the other side of the fence. Shmuel is a different story, He also shelter Bruno. Shmuel hints at things and reveals what happened to his home and family but goes no further. There are a multitude of boys at the camp, but they are kept isolated. This would account for Shmuel's remaining innocence.
It is possible for Bruno and Shmuel to have fun together and maintain their friendship in the midst of their circumstances by them both going to the wire fence everyday and Bruno would bring the chess board or a ball, anything that he thought they would be able to play with. Bruno also brought Shmuel food because he didn't get fed on a regular basis.
Bruno justifies his friendship with Shmuel by claiming that he has found a friendly Jew. Because of his age, he mainly notices the good parts of different situations.
In this story, the barbed wire fence not only represents the physical separation between Bruno and Shmuel, but also the racial, cultural, and political separation.
The only difference is that Shmuel was born a Jew and Bruno was born German. Their situation is born out of the tragedy of Nazi Germany in WW2. The author has used innocence to describe atrocities that are indescribable, to create a story of two boys who in their similarities and their friendship question the cruelty of humanity in a way that causes the reader to see the world through fresh eyes. Innocence is extremely important in the plot of this novel not only because of the subject matter, but also because if Bruno had better understood what his father's job was and what Out-With truly was, he would not have found himself in the situation that led to the climactic final of the book.