Seein the boy so sad about it was depressing as well. It was sad that the boy and the rabbit couldn't be together at the end, but the fact that the rabbit got to go and live with its own kind made me feel good. Children's stories deal with a lot of different subjects. Whatever the motivation, the point of most children's stories is mainly to entertain. A successful story has to be vivid enough to hold a child's attention, as well as get their imagination working.
Interesting characters are also important.
If a child doesn't find a main character interesting or empathize with them, there's really no point to them reading the story. It has likeable characters, such as Rashid and Mr. Butt and a young hero in Haroun. Children love when the hero is someone they can relate to.