We don't watch the TV show because I am not even sure it's on any more. But the first book DS ever memorized was Baby Elmo is So BIg, and now I have just bought him farking Winter Spring SUmmer Fall because he saw it in a charity shop and just kind of leapt at it, and now he is utterly hooked on it.
I mean, yes, OK, cute characters and nice simple learning-to-learn vocabulary, but why is it so appealing, so much more than other stuff?