We have children's books fairly nailed in the digital age and we have colouring in and paint and so on, but I am not sure we have got interactive children's books right yet.
I want to see a children's book where on the first page it asks what type of story do you want to read? Happy, sad, silly, etc...and then as the story goes one gets you at add things to it. What colour was the car? What did Susan look like? If it was well done you could have a child creating their own story each time and exploring their options.
If it was really well done, an interactive book could teach the child all sorts of things. It would be especially fantastic for therapy. A child that is sad and angry about being bullied at school could be shown alternate ways to deal with it. In fact just about any state of human interaction has alternate ways to deal with it. We just tend to get good at one of them and stick with it. Being shown multiple ways at a young age could be extremely helpful.
What an interactive book really needs to be though is fun. I remember being sad when I learnt to read because suddenly there was only one story. Before reading I had a new story every time I picked up a picture book. Maybe this way kids could have the best of both worlds.