What additional evidence does the author provide that suggests Bruno has no idea what really goes on at “Out-With” as he calls it?

Bruno goes to the camp and strikes up a friemdship with Shmuel, a boy in the camp. It is not until much later in the story that Bruno truly understands the nature of the camp. Bruno and his sister also speculate on what the camp is when looking through the window. They think it is some kind of farm.