I WANT TO TOTALLY BLOCK YOUTUBE FOR MY SON'S CHROMEBOOK

I have the same problem as many other people here and looking at this forum this is a problem for the past 4 years that you guys haven't fixed. A total SHAME. Let's start by this, I'm not interested in the TV streaming, I'm interested in laptops/chromebooks. My son is not even using VPN's, he's not that knowledgeable. In xfinity app I set up a profile for him, and then I set parental controls as ON. There's no other option in the app, it says that Xfinity is working with a third party yadda yadda yadda. I simply do not want my son wasting time with YouTube, I don't care which video, if it's child friendly or not. He's not watching porn, he's just wasting his time. I WANT TO TOTALLY BLOCK YOUTUBE ACCESS. Then I try the 10.0.0.1, even though your instruction says it won't work with my router which is the XB7. I use block words, I block the website and GUESS WHAT, I could still access it from his chromebook. YOUR ROUTER DOES NOT BLOCK ANYTHING. CAN YOU PLEASE SOLVE MY ISSUE? It's simple, just say "OUR ROUTER DOES NOT BLOCK WEBSITES" and I go and get your router back to the store and I'll get one that does the job. Thanks.