If your control doesn't establish some sort of control PDQ, someone is going to get hurt. I don't think the county will take anything but a dim view of things if such reckless behavior continues.
And, just to mention - it apparently does no good to yell at those kids. It's their parents you need to yell at. When my family were members of our local roundup club, members could be banned from riding at events for breaking the rules. Families could be banned from the club if their behavior, or their kids' behaviour, was a problem.