Bandlab is free, and you can create and produce professional level tracks with it, except for the fact that the output will be in mono. At his age I would expect inputs to be really just one maybe two input types. But that's where you could jump in and create things based off of what he created as a starting point. Then you can get 5, 6, 7 inputs deep on the instruments layered and looped.
Children are inherently good at creating beats for looping because they tend to stick with the same sound cadence so naturally you'll be able to layer things over top of one another without scaling. This makes it much easier to create tracks as they will stay in time.
Golf On Mars is a pretty chill, 2D golfing game with no discernable ending. You can play one hole at a time, or hundreds. There's cactii and rocks and water and other funny stuff that may or may not really be on Mars, but adds a bit of variety to the golfing.
It's a sequel to the equally fun, but sometimes maddeningly difficult Desert Golfing. Golf On Mars has a few changes that make it less frustrating if you do happen to get stuck.
https://play.google.com/store/apps/details?id=com.captaingames.mars&hl=en_US&gl=US
I kinda like Clash Royale, kids got me into it. Sorta chess like where you have to out think your opponent and try to gain elixar against their cards
