I've been trying Jami with family for a bit now and it's working fine so far. I use it on Linux desktop and they on Android phones.
It's an open source app that isn't yet claiming to be stable though. There may be troubles. The more people who use these kinds of things the better they get. P2P networks need peers.
It's a promising tech. The kids should be able to mostly communicate with it even if it craps out sometimes. It's in a pretty usable state for where it's at actually