Things never change.
If I ever see myself on film from 20 years or so ago when my son was in kids wrestling and I was a matside dad/coach I'm embarrassed to think I ever acted the way I did...screaming and hollering, which I probably thought was coaching. And I was far, far, from the worse. I didn't bother the parents of other kids and tried to act calm most of the time afterwards. Wrestling is a very personal, close, and exciting sport, and its one-on-one so when your little boy (or girl) is out there its just too emotional on some parents to handle. Even more so, I think, as the kids gain some success and expectations rise. Wrestling is one of those sports that no matter how good you are, somebody can, and probably will, still beat you.
It would be a whole lot better on everyone if parents would stay in the stands and cheer from there. Now, I know that's never going to happen. The next best thing would be for every kids club to have a "what we expect of our parents, coaches, and fans" discussion and repeat that pep talk a couple of times during the year. And, for parents that are pretty crazed (as I was) have the coach or team president have a friendly chat. It might not change the person's behavior entirely, but i might tone it down.