Hello!
Very neat concept! I would not have thought of it myself and I think it's a create way to teach math to young kids, it could even be expanded to do more than just +/- 1.
However, I did notice that sometimes my dice wouldn't collide correctly. Occasionally they would either pass through the wall completely, or get stuck inside the wall. If you plan on continually development, that is something I would look into fixing. But overall, nicely done!