Otherwise, some routers allow you to set up separate rules for 'guests', which authenticate with different credentials. You'd have to do some research to find one that had different DNS policies for each zone.
A simpler, though more expensive, solution would be to just buy a second router for your kids to use, then connect its WAN port to one of the Ethernet ports on the main router.
You could, of course, just modify the hosts file to block youtube.com on their local machines, but that wouldn't affect mobile devices, and they'd eventually workout how to get around it.
Otherwise, some routers allow you to set up separate rules for 'guests', which authenticate with different credentials. You'd have to do some research to find one that had different DNS policies for each zone.
A simpler, though more expensive, solution would be to just buy a second router for your kids to use, then connect its WAN port to one of the Ethernet ports on the main router.
You could, of course, just modify the hosts file to block youtube.com on their local machines, but that wouldn't affect mobile devices, and they'd eventually workout how to get around it.