Have you ever heard of HyperStudio? It was a great way for students to create web-page-like presentations that easily allowed the user to create links to other pages within the document as well as link to outside sources (primarily web pages). We may not have HyperStudio on our iPads, but we do have Keynote and we can effectively do the same things, and more.
Below is a link to a screencast video that shows how to create an interactive Keynote on iPads with additional directions for adding sound files (music, sound effects, recorded voice).
https://drive.google.com/open?id=0B44ILZlwbJoxSmhKenRjX29KYkE&authuser=0