Social media != the Internet. It would make it harder to sign up for an account with the large social media services covered by the law. They would need to check ids, or outsource to someone who does.

It would be like creating a bank account.

You could do plenty of other things. Anything you don't need an account for isn't covered. Depending on how the law is implemented, perhaps many forums wouldn't be covered?

I think it would result in kids going to websites that their parents haven't heard of yet and don't check ids.