Excellent set of links, thank you!
We have Ubuntu running on the kids' laptop. Big fans of TuxPaint and TinkerCAD, and yt-dlp.
We run our own Minecraft server.
They use Firefox browser with DuckDuckGo as the search engine.
When really little one of them was highly motivated to assemble a Raspberry Pi and peripherals to play Sled Dog Dash
They are really good at choosing pseudonyms for online accounts and interactions, like in Outschool classes.
The challenge is convincing their schools not to use their full real names associated with their school accounts. This is often more successful with small independent schools, but you have to catch them early before they set up the account on Google Classroom.