+1 for Linux but use your MacBook Air. There are Educational Linux versions that would be a great environment for your kid to learn to code. It can also be set up with kid safeguards.
You can also run Linux from a Usb if you’d rather not install it over MacOS
I recently put Linux (Mint) on my old 2015 MacBook Air and it’s been really great.
For OP’s question (just to stay on topic before we veer off), would you still recommend a Linux distribution on their MacBook Air?
Edubuntu seemed like a good choice to reuse their existing hardware and have a safe environment. There’s lots more choices to choose from
I’m only casually using my Linux MacBook but haven’t had any troubles with the keyboard.
Although a nice tiling window manager sounds like fun. I’ll have to look into it.