At the moment Star is entirely hooked on the book called "My Two Book"
This is actually just one book in the series. There is also a series for the alphabet. We haven't received them yet, but have ordered them from the inter-library loan. I was a bit skeptical, because I couldn't believe that there could be an entire book based on just one number. We found this book to be engaging and fun. It's definitely worth checking out from the library. I have been catching Star counting a lot more now that we've been reading these books.