A few years ago when the Captain Underpants series was becoming popular, I recall that some parents were complaining about the increasingly sarcastic, scatological content of children's books. In a bookstore I bumped into “junior chick lit”: Barbie-pink paperbacks in nearly monosyllabic prose that belies their cynically fashionable, prurient content.

Our family has an opposite problem. Jessica started reading alone at five and hasn't looked back. She works out syntax and pronunciation effortlessly and reads a newspaper without stammering—even if she doesn't comprehend the story.
When Nathaniel was six, choosing books at the library was like a math exercise. He carefully counted pages and estimated the words-to-picture ratios of books with numbers on their spines. Jessica, however, just peruses thick paperbacks from the spinning racks.
So we need to locate Captain Underpants' nemesis: writing with fifth-grade syntax that appeals to a wide-eyed first-grader.