This is going to end up at the Supreme Court probably sooner rather than later. The only reason it hasn't yet is that the justices usually wait for two circuits to rule definitively in contrary ways before taking a case, but Kavanaugh, in a statement respecting denial of cert for a similar law in Mississippi last year said that banning minors from social media was likely a first amendment violation. I would expect given that there are precedents that the first amendment protects both the speech of minors and anonymous speech that in the end these laws will be struck down.
I support this legislation. It's a wonderful demonstration for children to learn that the state can strip their fundamental rights at will.