Science has shown us that animals are intelligent beings (many species of animals experience emotions, have relationships and social structures, some studies even find animals displaying imagination and deceit).
But the specific intelligence of animals may be difficult to express to humans. So when childrens' books or movies give animals human characteristics, they are merely translating the animal's mental, emotional, and social worlds into human terms. Anthropomorphism can be seen as a translation of animal characteristics, not an artificial application of human characteristics onto animals.
Marc Bekoff makes a similar defense of anthropomorphism in Animals Matter. Responding to Wittgenstein's claim that "If a lion could talk, we would not understand him," Bekoff writes
"In order to talk about the world of animals, we have to use whatever language we speak. So, when we want to describe what an animal may be feeling, we tend to use the same words that we would choose to describe our own human feelings or intentions" (38-39).
I think the benefits of anthropomorphism extend into childrens' literature, television, and film.