I like how this is looking. I can try to comment on the "end user" aspect for you. I am the parent of a 5, 3 and 2 year old. The older two are definitely into learning games, but these are all web based and able to run on a cheap old Intel-Atom based machine. (I haven't actually tried my LE based project on it, yet).
This is definitely something my 5 year old would find interesting. He likes games and he likes Math and this is right up his alley. Watching him game, the advice I would have is that you should avoid very difficult twitch based elements. IE pushing rocks around to get 13 is fine, but aiming and firing a crosshairs should be out unless the target is relatively stationary.
We hear all the time that TV and video games is harmful for or kids. Not to get on too much of a soap box, but our family's feeling is that is mostly a bunch of hogwash. Yes, 8 hours a day in front of a TV or computer is terrible, but a few hours every other evening is fine. Our kids have learned a great deal. My 5 year old is in Kindergarten and is ready and doing math on a first grade level. My 2 year old can sign his alphabet and knows all the letter sounds. This is just phenomenal and modern media deserves some of the credit by offering engaging learning programs. Also, my kids choose outside over TV still. The recent heat wave (that just broke here in Missouri) killed any outdoor activities.