I have 3 kids, all around the same age (K/1). They all got laptops about 18 months ago for christmas. I installed mint linux on all of them, and installed a few free/libre games for them to play, and I self-host the game server at home.
One game they play is luanti (formerly minetest). I gave them instructions on how to clone the git repository for the game, run the build script, and then start the game. They've probably forgotten the build instructions, but they know to play, they have to type `cd code/minetest` and then `bin/luanti`. Occasionally they have to run `git pull` to update the code on their computers. I handle all the game server administration.
I initially blocked all internet access with a kill switch, but this quickly became an issue because you need to be able to run `apt update` and a few other commands to keep the system up to date. So now I run a proxy server called e2guardian that lets them access sites that I choose.
Later, I introduced them to scratch, and I downloaded the entirely of griffpatch's youtube library with yt-dlp and organized it into folders on each of their computers. I've done the same thing with other tutorial style videos. They don't have access to youtube, and I don't really think it makes sense to give them access at this age.
They run scratch locally, as opposed to using scratch.mit.edu. I enabled the scratch website for a couple of days as a treat for them, and as expected, they spent most of the time exploring and playing others' games, but very little time building their own. I sort of expected this to happen, so we closed off access a few days later, and they took some of the ideas they saw online and started playing with them locally.
So my experience is:
a) linux makes a great platform for kids, since it's very easy to tweak things to stop behaviors that you don't want to reinforce. e.g. `sudo chmod 400 /usr/local/games` turns off all the games, `sudo killall kidname` will close the desktop session if your kid isn't listening when it's time for bed, you can set up time-based login policies with pam_time, you can install your own root certificates for SSL MITM, etc.
b) games reinforce that "computers are fun", and games like luanti are free, open-source, and hackable.
c) interest in games naturally spills over into interest in making your own games.
If you want to try luanti/minetest, I recently cleaned up/released a mod that I built for the kids last year called turtlebots. It's a visual programming tool that lets you program little turtle-shaped robots that can navigate in a minecraft-style world and build things as they move around. Source is here: https://github.com/jmole/turtlebots