If your tween has access to a smartphone, or even an old one that can still do wifi, you can text onboard using the
DCL Navigator app. Also, each stateroom receives 2 "wavephones" that call or old-style text onboard, and if needed you can rent another from Guest Service.
There are CMs in Edge. Kids sometimes hang-out at Edge but also they have "out and about" activities which will take place outside of the actual Edge space. And they often head up to get a snack on the pool deck. So yes, to attend Edge your tween will need to have sign-out privileges. Many families find that setting rules ahead of time and talking about expectations as well as consequences works out well. Rules such as "never go into another stateroom and nobody invited into our stateroom" and "always call/text parents when leaving Edge" or that the kids must meet up with the parents if leaving Edge, etc.
If you have concerns and do not want your child to have sign-out privileges, you can restrict him/her to the Club/Lab.
Enjoy your vacation!