There was this amazing talk called "juice it or lose it" that's meanwhile a little famous among game devs that I would recommend watching with him [1] because it shows how much of a game is effects, tweening and animations.

Of course, he's 9, but maybe this will help him understand how to polish things like this and make them more fun to use?

[1] https://youtube.com/watch?v=Fy0aCDmgnxg