I love slack. It is possibly one of the most flexible group-chat/productivity tools. I use it work all the time so figured it would be fantastic if all the kids could learn to communicate better and get a touch of the professional world while doing it.
We have a Slack workspace for the kids where we have created several channels. It is available for mobile devices including tablets so parents and kids can communicate with each other during the week.
We are also using it to keep track of what was done during the week and give out assignments to the group or individuals. You can also add some pretty cool plugins for task assignment etc.
Best of all, it’s free for a group like ours.
If you decide to run a group of your own, I would highly recommend it for communication.