Actually, Bruno knew it was not a farm. Gretel told him that was a possibility, but they both agreed that there should be cows and pigs and horses if it was a farm. If they grew food, the ground would look a lot better. (page 34) . It isn't until chapter 19, when Bruno enters the concentration camp that we find out what he expected to see. In his imagination he thought that there was going to be a lot of happy families sitting around in rocking chairs and telling stories about how things were better in the good ol' days, and how they respected their elders more than the children of today do. He thought that the children would be playing with one another the games that children play: football, hopscotch, and tennis. He had an image of a shop in the center of all the huts and maybe a small cafe and some fruit and vegetable carts like they had in Berlin. (pg 207) He saw none of this.
A farm, He believed that the place outside his window was a farm and that all the people wore pajamas.