If they really wanted to block access to adult only material, and not be a surveillance state in the process, the correct solution would be that every home router and every cell phone plan would have a secondary password that had to be entered in order to access that data.

Then by default only the parents and the people deemed responsible enough to have access to that password would be able to view adult only content.

That is very secure, it would sweep the floor with a huge percentage of successes with a minimum amount of intervention into people's daily life.

Sure, some kids will get the password one way or another and view adult only content, but at least they would know they had to go through the extra steps to do something they weren't allowed to do.