Girl, 10ish: Dad, they have Tales of Beedle the Bard! That's in Harry Potter! That was in Dumbledore's will for Hermione! I really want to read it!
Dad: Come on, that's awfully thin. It looks too easy for you.
The book stayed unbought.
Putting aside the fact that length and challenge don't always have a direct relationship, so what if the girl had read harder things before? She was excited about Beedle - excited, in fact, because it would have told her more about a series of gigantic books that she'd presumably already read. Where's the problem?
Not every book a child reads has to be a "step up." Adults who've read Shakespeare are allowed to read Danielle Steel or the comics or whatever else catches their fancy. Reading doesn't always have to be work.
I wish there'd been a good point to jump gently into the conversation, but alas, I didn't find one. Kid, see me for directions to the library.