Animal Farm is mockingly disguised as a children's book, when in reality it's far from it and everyone knows it. Narnia and A Series of Unfortunate events (although I have little experience with the latter) are, indeed, both children's books, but this doesn't prevent them from being decent stories. Nobody was really questioning the capacity for good literature within children's books. Hell, The Hobbit was made for young children and it's now considered very good literature.