Gretel calls their new home „Out-With“ (p. 24). Why do you think Boyne chooses to have Gretel call the place this?

It is actually Bruno who calls the camp "out-with". He misinterprets the word Auschwitz. It is actually Gretel that explains his mistake to him,

It's not called Out-With, Bruno,' she said angrily, as if this was the worst mistake anyone had ever made in the history of the world. 'Why can't you pronounce it right?'" (pg 181)