Nice job. I think it would be even better if there were some kind of visual reward for getting an answer correct or not. I tried Quick Play, and I had to fill in every single cell and then hit Submit before I could see what I got right or wrong.
Kids really like that kind of visual feedback (confetti or something similar).
Years ago I wrote a little edutainment game called "Aladdin's Mathemagical Flying Carpet" to help teach my younger siblings the multiplication tables which you might also like. It takes a much more gamified approach.