Maybe instead of preventing him from tinkering and breaking it, set up a safety net so he can tinker without fear. For instance you could configure the device with config management that will reset the system back to a usable state, or put it all on a filesystem like zfs that has snapshots, or create an image of the system and reimage it when it breaks.

Open Emu might be another good option. Also, there must be a wasm emulator system around somewhere that runs entirely in-browser.

In most modern Linux distributions, you could preconfigure retroarch and whatever else first, then set the filesystem to read-only, while mounting an overlay filesystem on top that is discarded at reboot.

The idea would be no matter how hard he breaks it, he shouldn't have Root's password and therefore cannot disable overlayfs

Look for the overlayroot package in whatever Linux distro you're most comfortable with.

This doesn't answer your question, but thank you for the love and patience you have for your son.

There's setting(s) in EmulationStation (in RetroPie) that can make it kid friendly.

https://retropie.org.uk/docs/Child-friendly-EmulationStation/

That said, https://batocera.org/ is a fork of RetroPie with a lot of sensible presets to make it quite a bit harder to break.

If you don't mind jailbreaking, the Playstation Classic appears to be going for about $100.00, and I understand it can run Genesis and SNES emulator a as well once jailbroken.

Another great option to consider is the Evercade VS: https://www.theverge.com/2021/11/25/22801139/evercade-vs-retro-console-review

And the HyperMegaTech Pocket - which does a terrible job advertising that - it plays the same cartridges as the Evercade VS. https://www.hypermegatech.com/

Evercade has a simple interface, and is easy to factory reset: https://evercade.co.uk/support-vs/

Evercade has a good mix of recognized retro (and new retro-style Indie) games available from Taito, Data East, Atari, Epyx, Team 17, and some real hidden gems from Gaelco, Jaleco, MegaCat, Toaplan, IREM, Piko, etc.

Evercade carts are about $20+shipping, and come with anywhere from 1 (new Indie game) to 20 games (Atari 2600) on each cart. More typically around 7 games per cart. About 14 news carts were released last year, and there's a bit more than 500 supported games so far. https://evercade.co.uk/cartridges/

Source: I'm a minor contributor to the RetroPie ecosystem and a huge Evercade fan.

Hmm, that's tough. Usually I'd recommend Ludo which is a minimalist version of retroarch that doesn't let you mess around much, but even then it's not hard to ruin the visuals or turn off sound from the app settings.

Maybe a combination of Ludo and locking the settings file like someone else suggested might work. This page and this page in the documentation tell you where settings files are stored.

Maybe look into setting up a retro pi. If you get the correct hardware you can use a wireless controller. I’m not sure about the settings that could be messed with, so you’ll have to look into that, but otherwise it might be a good solution.

A few ideas:

https://atari.com/collections/hardware

https://www.amazon.com/Flashback-Anniversary-Controllers-Not-Machine-Specific/dp/B0BGYD6GM9

I have a few of the Flashbacks and an Atari gamestation pro. These might meet your needs.

ETA: Sorry, I'm kind of rushing this morning and didn't read your entire post. Some Flashbacks do use wired controllers. I picked up a couple at a thrift store for cheap. I've only used my gamestation pro on a table which makes the line of sight thing pretty easy (for me).

If I may add a different suggestion: have you considered hacking one of the old consoles that you have/can buy used to enable retro gaming? A used Wii or Wii U for instance have great wireless controllers available, especially used Wiis without the games and accessories are dirt cheap. The process is very simple, just do a quick google. Basically, hack an old console, load the ROMs you have, get an appropriate wireless controller (8bitdo makes A LOT of compatible wireless gamepads), and you're good to go.

Here is an example, for the Wii U, though the Wii is probably even easier (but SD)

https://youtu.be/HRXwzGh-FoY?si=EG6HfJHcOGiJvrEs

You could also get the games using the virtual console offerings for the Switch if you don't want to mess with ROMs. I know the switch has that adapter thing that holds the nunchucks in a 'classic controller' gamepad form. Even very old consoles sometimes have great retro gaming or homebrew options, the classic Xbox to name one example.

All in all I think this would be the fastest and maybe even cheapest option.

Also, kudos for nurturing the love of video games in your son.

Get one of those locked boxes like Target or video game rental places had.

I just got an R36S for ~$36 shipped from Alibaba. It’s awesome out of the box, but you can tweak. It’s incredible what it can do at that price.

To son proof it, just grab an image of the SD card before he starts mucking with it. Easy to flash back to a known-good starting point.

You can even back up his customized version when he has it mostly working before he mucks it up again.

The Pyra Handheld - Just buy a few extra SD cards and swap out the SD card with a working one after he breaks it.

Edit: Never mind, it's still under development, I thought it had been released.

what about a docker image to spin everything up? that way you could just restart (which would load up the default configs)