I gave my nephews "air-gapped" laptops (old ThinkPad t430s). Technically they're connected to the internet, but the hosts file blocks so much that even if they could figure out how to get past the locked down KDE desktop, find a terminal, install a browser and open it, they still wouldn't be able to access anything. I downloaded block lists for ads and porn, and manually added social media sites. However... They can still join my xonotic server and play against each other. They have a bunch of games that work on LAN (one creates a server, the others join). This includes Minetest, which they find indistinguishable from Minecraft. So they've completely stopped pestering their parents to buy them consoles and phones that are "forcibly online". I suppose they're lucky that there's three of them to play together. Lone kids couldn't do this with their friends without multiple families getting together and sorting it out.

I'm going to follow this up with cheap phones that I can lock down. I'll add a bunch of hand-picked games and maybe set up a slack account and get their friends to join. Then disable the play store. Again, this will shut them up for a while and let them have access to technology without the brain-rot. And their parents will be in slack, so they'll be able to keep tabs on them. (I don't have kids, so I have the spare time and the inclination to do this, unlike their dad)