I don't have much to add to Charles' post, especially since I share his mixed feelings towards both the Little Lit anthologies and the TOON series. I suspect, though, that kids might be more enthusiastic about these books than us crabby old adults are.
Take my kids, for instance. In 1997, when my son Nate was less than six months old, I bought Art Spiegelman's Open Me, I'm a Dog (1997), a children's book that in retrospect seems like a practice run for Spiegelman and Francoise Mouly's "Raw Junior" direction. I found (and still find) Open Me cute but unsatisfying. Spiegelman's painted art in Open Me is considerably less accomplished than his pen and ink work, and the dog-is-the-book situation, while clever, pales in comparison to the deeper self-reflexivity in kids' books like Chris Van Allsburg's Bad Day at Riverbend (1995) or David Wiesner's The Three Pigs (2001). (Eleven years ago, I hadn't read Van Allsburg or Wiesner yet, so I evaluated Open Me in light of Spiegelman's career; like Spiegelman's illustrations for a new edition of Joseph Moncure March's The Wild Party , Open Me felt like a pretty anemic follow-up to Maus II .) A couple of years later, though, I read Open Me out loud to my post-toddler son, and he loved it. For about five or six months, we read it together at least once every day, and occasionally I'd see him dragging the book around by the leash or sucking furiously on its corners. He loved that book so much he sucked the crap out of it. For Nate, Open Me was his first encounter with metafiction, with a narrative breaking through the fourth wall, and he found it magical.
A similar kind of magic happened when my daughter Mercer, who's seven years old, recently got her hands on the TOON books.