Hello @StevenHart965
The scheduling feature in Google/Nest WiFi uses the "MAC" address that each computer has on each of the interfaces it can use to connect to a network. So, for example, your son's computer has an Ethernet port and a WiFi interface. Those each have their own unique MAC address. So, it will show up as two different devices (perhaps with the same name) in the Google Home app's WiFi device list. You should be able to add both of them to a schedule.
All of that said, if your son ran an Ethernet cable in order to get around a schedule, he likely knows (or can easily figure out) how to change the MAC address on either the Ethernet or WiFi interfaces in order to get around the restriction another way. I found using Microsoft's "Family" feature to be more effective in terms of controlling screen time. Apple has a similar feature called "Screen Time". These work at the operating system level, and while they aren't perfect, either, they are at least more effective tools than trying to solve this at the network level.
