Thanks all, I set up a mumble server on a local Montreal host. We're currently using a realm to play but I might switch it to a full fledged server with the same guys.
A lot of the suggestions I liked on paper, like Revolt or Matrix and might take for myself. But the fact that there were community servers access directly in the app and no way for me to regulate their visibility for my kids instantly disqualified them for this specific use case.
With Mumla they only see the server I set up for them and I can control who comes in.