If you are running iOS 14 it uses a new feature for Wifi called Private Address by default. It's there to keep your device from being tracked across different Wifi networks. I turn it off because every time my devices re-connect it assigns a new MAC address which I find annoying because it interferes with the nickname I assign to all the devices on my network. In a nutshell, to eero it's a new device. I wonder if your children are using this feature to get around your pause restrictions on their devices? You might want to try turning that feature off to see if that helps.