The zoo is overpopulated with humans and with animals. Everyone seems to be pleased. Specially animals. The forest is a taboo. No one dares to go to forest. Couple of kids accidentaly end up in forest. When it turns out no one comes to save them, the kids start to build themselves a machine that will help them out of the forest.
Total urbanisation has entered into the mind of wild animals. It seems that it is unalterable.