I wouldn't purchase one of these, personally. The point of books for children is not to turn them all into a video game. I wasn't impressed by the reading either - I think that the BBC do it better with their various story time programmes. Reading stories isn't about having a machine speak the words on the page.
If I wanted to design an ebook for a child, it would simply be a large colour ebook. I don't think that the technology is cheap and robust enough yet to make it attractive compared with DTBs.