Even if we assume children don't find a way around this, they will simply switch to a different social media app after their two hours are up, or switch to an app that doesn't have the two hour limit at all.
This is clearly a rule that would have to be mandated by the government, or perhaps parental controls on their devices (not sure why parenting was ruled out here apparently). Same with whatever opinions people have on an algorithm showing you content you'd enjoy, which has always been the goal of media since the concept of a magazine was created, they just didn't have the right tools available.
It also will only punish kids who actually gave their age no? That's not actually required (yet) to sign up for a social media app. I was probably 9 when I started clicking a random year for my age when signing up. Doesn't take you long to figure out you have to jump through hoops when your honest.
Really I have no idea what this case accomplished besides being a tax on a successful company.