How utterly strange. If a book is too difficult for a child, presumably he'll figure that out in short order by actually reading it. Why would the librarian even intervene at all? It's not like an elementary library will be stocking erotic or graphically violent literature.
This has been our experience. DD was 7 when she finished reading Harry Potter independently and decided to move on to Hunger Games... but HP had been bedtime stories since she was 5, with her looking over my shoulder, so all of the harder words were familiar, and I'd had a chance to explain anything new. She came across too many unknown terms in Hunger Games (she pointed out "apothecary" as an example), and she decided to move on to something else.
I think that librarians are often trying to protect the children from a confidence setback. DD did have that kind of experience, but we were quick to point out how quickly she was learning, and that this book may be too hard now, but that's only a temporary condition.
Fast forwarding two years, she probably finished off Catching Fire last night before lights-out.
