The one thing I don't see and always wonder about with these sorts of things is how they define "social media". Seems like a tough thing to do - if you cast too broad a definition you'll end up with just about anywhere one can communicate on the internet, including email. If you take the very narrow approach of naming FB, IG, TikTok, etc., you almost certainly miss out on whatever the next platform is that's relevant to kids.
Remember YikYak? IIRC that was worse for kids than most of the big social media sites, but how do you write a law that anticipates the next YikYak without banning everything?
I don't think it really matters if the definition is too narrow as long as you ward off the worst threats. An easier way to classify them would be by size: any social network with over 1000 users should have to regulate their users. So as soon as something starts being relevant from a public safety perspective it'll fall under the law.
Remember YikYak? IIRC that was worse for kids than most of the big social media sites, but how do you write a law that anticipates the next YikYak without banning everything?