Becoming an adult means leaving the world of your parents and starting to make your way toward the future that you will share with your peers.
Putting together philosophy and children would have been difficult for most of history. But very fortunately for me, when I started graduate school there was a real scientific revolution taking place in developmental psychology.
Young children seem to be learning who to share this toy with and figure out how it works, while adolescents seem to be exploring some very deep and profound questions: how should this society work? How should relationships among people work? The exploration is: who am I, what am I doing?
Animals are certainly more sophisticated than we used to think. And we shouldn't lump together animals as a group. Crows and chimps and dogs are all highly intelligent in very different ways.