I'll respond briefly:
I think this is bad policy. It seems to be based on the assumption that "the demons are outside the walls" - that the internet is a medium through which evil enters the home. Whereas my belief is that, a significant percentage of the time, the evil is already inside the home, and the internet offers a means of (partial) escape, if not a means of calling for help.
During my last years of highschool, social media was very much in it's infancy (ICQ, MSN, and the like). Thankfully, the internet was so brand new that parents hadn't yet been taught to fear it, so me and my peers were able to use it with a lot more freedom, and less scrutiny, then modern kids enjoy.
It gave us a chance to speak freely about our problems, in a way that we would never have been free to do in the presence of an adult. I'll never forget one night, while I was in an MSN chat, when a good friend of mine confessed that she planned to commit suicide very soon. It was a conversation that could've only taken place on the internet, as there's no way we ever would've felt safe enough to have it in the schoolyard, with all those tyrannical, judgemental adults lurking around every corner.
I know it was a different time back then, but the internet wasn't the source of our problems; it was a possible avenue of rescue. The anguish that plagued us didn't come from the internet, it came from our own cruel parents! The suicidal girl I mentioned earlier? Her mother was a notorious monster! Micro-managed every facet of her poor daughter's life, even at 17! My family life wasn't a whole lot better; and neither were many of my miserable friends'.
There seems to be this new fad kicking in now of painting society and it's government as the great evil threatening kids, while lifting parents up on a pedestal as these heroic defenders of kids and their wellbeing. But my experience has taught me that parents can be the most awful of things; and that this is a common enough phenomenon that we shouldn't just dismiss it as being some trivial side-issue.
It truly sickens me to think that we are sealing kids up, in their own awful homes with these monsters, with little if any means of reaching out for help.
Aren't we supposed to be a society that cherishes free speech? I say we let the kids speak; and we aren't doing that if we prohibit them from the platforms that give them the only serious chance they'll have of being heard.
Dolly Everett supposedly said: "Speak, even if your voice shakes." The government just told her modern peers: "You have no right to speak."