

Another vote for scratch. Most kids that age want quick results and not to spend ages debugging something. Funnily enough I’ve seen the same scratch interface used to program industrial robots.
How much time one on one are you committing to spend with the child? This will make the difference.
Alternatively, think about some sort of robotics kit. Doing stuff in software is great but if it changes something in the real world, even better. Have you thought about something arduino?
Just for balance though, make a raft, a treehouse, a tent, make a fire without matches. It’s all problem solving but I bet any kid will remember getting muddy more than writing a neat while loop.
Surely the simplest approach is not to use a wifi ssid that you don’t trust. Yes, mobile broadband is slower and more expensive, but is also more under your control, it is however harder for your boss to monitor.
If I was an it manager I’d probably want to keep an eye on WiFi traffic, even on the open ssid, just to see what’s going on. I don’t trust free WiFi.
If you can’t use 4/5g, and can’t find a suitable firewall or VPN, can you set up a different user on your phone? - and be disciplined in is use.