Meta is not blameless here. Responsibility can be shared when Meta (and others) are essentially preying on children. It’s an uphill battle for parents by Meta’s design.

They’re not Meta’s kids, they’re freemium customers.

Sure, parents do bear some responsibility here too. But we are talking about a platform that is engineered to be addictive to adults too. So it’s not as if the platform isn’t still predatory even if we find a way to parent every child on the internet.

Doesn't this lawsuit (essentially) prove otherwise?

It would work if parents had legal course to seek justice against corporations that stalk, groom, and manipulate their children against their wishes.