I was thinking Jackanory style "programs" where authors read their own book or a voice actor reads. Indeed you could probably by rights for audio from the BBC, etc., or from Barefoot Books, say, and match up with the book. Very easy to establish a large catalogue of books then.

Another extension might be to offer a copy of the book with an audio-CD/mp3 of the person reading bundled with it.

I think there are so many variations possible (particularly in education sector) and that this idea will be in demand from children's publishers (licensing?) that you should do well with it.