I know K-12 educators who post videos primarily for their students and fellow local teachers, and they disable comments and voting because bored kids will fill the comments with crap, and scammers will target the kids.
Yes, but cause and effect are reversed from the teacher's perspective. They mark the video as "made for kids" because that's the easiest way to disable comments.
It's required to mark the video as made for kids if it's for kids.
Yep. This sabotage is exactly why K-12 teachers disable comments.