Kids winning the battle on Youtube - Need to show who's boss

So the time as come to put the foot down on the Youtube App inside the Optik TV STB.  I was able to block the YouTube channel with PIN so victory there. From what I can tell there is no way to uninstall the YouTube app on the Optik STB operating system. I have called tech support and they said they can't uninstall or block the service. It's cooked into the operating system. 

I have got a secondary router acting as a wireless access point (ASUS AC66U) that is connected (wired) to my Optik STB. The AC66U router is wired connected to main router. The WAN and DHCP is disabled on this router as well. I have flashed dd-wrt firmware (v3.0-r42617) on the router to replace ASUS firmware. I have turned off the wireless (2.4g/5g) on the router as I just want to block all Youtube content via LAN port. I have the MAC address and IP of the Optik STB. From investigating on google, it seems the magic happens on a menu called "Access Restrictions" within dd-wrt. I entered the MAC address/IP address that I want to block/filter within a section called Access Policy. In addition, I put everyday and 24 hours under "Days" and "Time". Under the section call "Website Blocking by URL Address I put "www.youtube.com". Under the section called "Website Blocking by Keyword" I put "youtube". I "Saved" and "Apply Settings". 

Unfortunately, kids are still laughing in my face. It's not filtering the youtube content when they accessing the app via Apps in Optik. 

I don't want to block netflix, or prime or other media apps. Just Youtube.

I know I'm on the right track but need some help. thanks!