I think it's a great idea for a kid's book! The rap-rhyming possibilities fit very well in with the theme of children's book writing. It's like Mother Goose ramped to 11, with a dash of groove.
Then there's that whole bit about giving kids something to identify with. The more, the better in my book. (no pun intended )
Already purchased for my 8 year old....he loves it. Of course he also has already recorded 3 mixes on my Techniques without computer aided BPM managment....yes I've taught him old school, pitch slider and all