I tried something like this. my kids just turned off wifi and I can't control the cell signals. Phone parent controls are not powerful enough for what I need
THIS. Incredibly frustrating that iOS (I’m not sure about Android) doesn’t provide a way to disable mobile data or Personal Hotspot as part of Screen Time settings.
If your kids are breaking the rules you have set for their phones, it sounds like it's time to take away their phones. One doesn't need a fancy modern solution here.
I am just asking mines after dinner to leave the phone after dinner to my office where all electronic devices charge during the night.