How to stop Mac spoofing so child can't bypass being blocked.

[DavidJBurger1]

How to stop script tool son is using to mac spoof to bypass being blocked at night?  If I put up a firewall it causes problems with his online gaming(I'm okay with the causing problems)  but it stops the rest of us from being able to do so.  ANyone have any suggestions on how to stop the mac spoofing?  He runs his script tool and it assigns a new mac address so xfi doesn't recognize it and allows it to connect.

[strega7]

My Netgear router (not a rented router) can be set so you have to approve the addition of any new devices. I don't know if any of the Xfinity routers have that feature.

[DavidJBurger1]

Which Netgear router do you have.  I may have to look into getting one then.

[strega7]

I have a C6900 which is a combined modem and router.  I assume their stand-alone routers have most of the same features.