It's optimistic to assume parents have direct control over whether their kids are screaming or not.

That's very true in general, but anecdotally the children in Korea (the few I saw) were very well behaved. They didn't shout, scream, cry or anything. Even when playing, running around etc. they were remarkably quiet. It's a combination of education and culture.

They have control over whether their kids are screaming where it will disrupt other people. You can always take a child into the bathroom or outside where you can resolve the issue without being a menace to other peoples' experience.