I'm trying to block YouTube for all the devices on my network, but it's not working

I'm trying to block YouTube for all the devices on my network, but it's not working. I've put in "https://www.youtube.com", enabled parental control, and made sure that all the devices are trusted=NO. But YouTube still comes up every time, ever after rebooting the device.

It's very important that I get this fixed, can someone please advise?