This concept of keeping children away from more difficult books seems so bizarre. I grew up in a home full of books and can't recall being restricted there, at school or in the town library, save for some books with quite mature content. (I wiggled around that some at home and am still slightly scarred by reading some book about nuns being killed in the Congo, probably at about age 10.) No one seemed to care that I might want books ahead of my grade level. The notion that teachers or librarians think they need to restrict something because it might be too hard seems like they are heading out on a fool's errand.