If we are talking about the hub they likely don't work
Like a IP but not a MAC is given pre set on the device to route at layer 2 between hardware done by a protocol called ARP note MAC's can do changed per device or even be random .
Like a MAC but not a IP is given by a DHCP server with a NAT router this is like 192.168.0.2 done at layer 3 the device can change its IP when the MAC is changed or a fixed IP can be configured.
I'd leave well alone, attempting to block devices has repeatedly been the express way to utter chaos on the home network with all sorts of kit not working and no clue as to why or how to restore access when the heating is not working or a business laptop will not connect over the office VPN.
If Parental Controls is what you seek, define what is acceptable use & set a good example.
