I assume practically the same in terms of child safety. Teens will find a way around or a more underground alternative to hang out with each other online.

To your question: More headaches and invasion of privacy for everyone due to enforcement. How do you enforce it other than state issued ID? It would also exclude a lot of people who either don't have that ID or don't have access to it. Then there's the whole question if whether you want the government to know what media you're interacting with. For legal reasons the social media company would need to keep evidence on file of your identification, if not report it. Keeping is regardless of whether it's part of that law, CYA and all.

Define social media and then imagine a constant argument of semantics where online communities get destroyed and created based on law suites.