Can anyone recommend a safe, private and secure way for my children to have a way to message each other? Some kind of Chat / IM… Their primary devices are iPad(s) so it has to run on iPad OS or it must be an installable PWA (cc @ @justamoment@twtxt.net in case you know of any PWA App here)

Ideally I would either like to be in control of the server-side – self-hosted with accounts I can control and who/what they are able to connect to, etc.

Or, completely local to a local network (i.e: p2p, wifi only).