Parental controls not working for most devices

My child has a serious problem with paying attention in school and I have since blocked youtube on my router. To test this, I didn't "trust" any devices and have since found that only a couple devices are prevented from going to youtube.

I've searched the forums and found a lot of other parents having this issue over the past year but there are no resolutions from comcast on solving the problem.

HOW DO I BLOCK YOUTUBE FOR ALL DEVICES?!