As somebody who is entirely for restrictions on internet / social media, I think you're missing the bigger picture here. First, you assume that parents have the technical knowhow to restrict their kids from specific sites. My parents used a lot of different tools when I was a kid, but between figuring out passwords, putting my fingerprint onto my mom's phone, and spoofing mac addresses, I always found a way around the restrictions so I could stay up later.

But let's assume the majority of parents can actually do this. The problem with social media is not an individual one! We've fallen into a Nash Equilibrium, a game theory trap where we all defect and use our phones. If you don't have a phone or social media nowadays you will have much more trouble socializing than those who do, even though everyone would be better off if nobody used phones. As a teenager, you don't want to be the only one without a phone or social media. And so I truly do think the only solution is with higher level coordination.

Now, it's possible that the government isn't the right organization to enforce this coordination. Unfortunately, we don't really have any other forms of community that work for this. People already get mad at HOA's for making them trim their lawn; imagine an HOA for blocking social media! I do think the idea of a community doing this would be great though, assuming (obviously) that it was easy to move on and out of, as well as local. This would also help adults!

So to be honest, I don't think parents have the individual power to fix this, even with their kids.