vipaal

Every modification and deletion is prevented regardless of the method, be it mv, rm or other commands on the terminal or through a GUI, with or without sudo until sudo chattr -R -i /path/to/directory is performed

I think looking into man chattr is a good option for this

Been a few years since using Emacs extensively. From memory, IRC is a good fit for what you are after for texts and some emojis. No clue regarding multimedia messages.

If IRC is acceptable

Make your own channel on say, Libera chat, set your own rules for how long those messages are retained. Make a user for each of your devices. You are set. I've used ERC a few years under Emacs. Also used GNUS for reading and writing emails from the big providers.

If the MacBook is an Apple Silicon Mn processor one, Asahi is the obvious choice

For other cases

My first suggestion would be to try the distribution you used in WSL

Second would be Linux Mint, can't go wrong with either of Ubuntu edition or the Debian edition

Third would be OpenSUSE Tumbleweed. Though a rolling distribution, with easy rollback commands, any unusable state can easily be left behind

OpenSUSE newcomer here, from decades of Debian and Debian derived systems.

I vote Debian with Xfce4 for the base system with Nix or Guix to let the kids freely install and play with software as required without requiring root. Stable release should be good. Testing release if time and resources to keep up with the updates are at hand.

Along with teaching the kids computers and software, please also consider teaching them how the Debian packagers, maintainers, developers, testers, admins, etc work and might never meet others in the project whilst releasing a great system every couple of years.

+1

And

In the off chance the files are not under git or some other VCS, might be a good idea to add the -b option to backup

https://www.opensourcealternative.to/ lists rocket.chat as an alternative to Slack and Discord

I have not used it. I have used Mattermost. And it can do channels, teams, hashtags, @ mentions etc similar to Slack. Though it requires the server be hosted and administered by you or someone you know.