Good children’s books are profitable for adults. C. S. Lewis put it like this:

I was therefore writing “for children” only in the sense that I excluded what I thought they would not like or understand; not in the sense of writing what I intended to be below adult attention. I may of course have been deceived, but the principle at least saves one from being patronizing. I never wrote down to anyone; and whether the opinion condemns or acquits my own work, it certainly is my opinion that a book worth reading only in childhood is not worth reading even then.