Parents can try the parent's control and monitoring software, but once the child (even the spouse or grandparents) gets the free smartphone through the data plan, good luck and let them speak in the family dinner.
Just as parents have the ability to cut Wi-Fi right at home, they should be able to cut off cellular signals if needed. Putting them on the phone with their hands in the airplane mode may not work properly, turn the house into a Faraday cage, it's just a very much only one that should try the tin foil hat. However, if necessary or needed, the indoor cell phone jammer should be an option.
All of these examples are based on other lines that can be used for emergencies, or at least some people want mobility sufficient to exceed the interference range. There is absolutely no way now, even those most meaningful people can use limited technology, will not disrupt the service, far beyond their classroom, theater, office or family range.
But before you finish, think about it, if you really get hurt, or maybe that time, no cell signal is the best moment of your day. Of Course, if your signal stuck, you may not be able to make a call.