Some of this summer's hottest new early readers are based on movies like Prince Caspian (PG), Iron Man (PG-13), The Incredible Hulk (PG-13), and The Dark Knight (PG-13). In fact, at many chain bookstores there is now a specifically labeled "At the Movies" tier on the early-reader rack.

This isn't the first time brand extensions have shown up in early readers—books starring SpongeBob and Dora the Explorer have been around for several years now. But there's something more unsettling about books aimed at preschoolers and kindergarteners featuring PG-13 movie characters, and they pose a tricky question for parents. Books like A Hero Called the Hulk and The Dark Knight: I Am Batman practically beg to be plucked by small hands.

As parents, we may bristle at what seems like a crass attempt to indoctrinate the next generation of Iron Man and Hulk fans (in preparation for the inevitable sequels). But what parent wants to stand between a child at the cusp of reading and the books that excite him? Plus, how bad could they be?