Persian Cat Press guest blogs at Teacher Turned Writer to describe their approach to children's books as apps. I linked to research about children and ebooks just recently, so this pracital example of books for children provides a good follow up.
An app is a unique platform in that it allows publishers to create a product that involves not only traditional reading and visual literacy, but also a physical and aural literacy too. In this way, apps have the potential to not only talk to a child’s imagination but also directly to their senses.
They talk about their first books-as-app, 'The Gift', and all the various elements, from musical scores to non-essential-but-fun little diversions in the text, that were brought together in the final work.
Check it out here for some inspiration: http://teacherturnedwriter.gillrobins.com/?page_id=108