This is more personal / parenting issue rather than technical...
- If one believes XFinity TV ads, you can control everyone access from a smartphone app.
- There are many companies that provide over-the-internet controllable power sockets (commonly called "smart plug"). I have one of these, and I can control it from outside my home with their Android / iOS app. Connect your router to it. When you go home, reconnect it (yes, kind of suicide...) But if your son understands how this work, he can simply bypass it.
- Check whether your router supports remote management over WAN port.