jurasketu

Here are my thoughts from a lot of experience in general child rearing and training children specifically in Aikido.

Humans are social animals, you need to "train" them with that in mind.

Connect to the students and measure praise appropriate to behavior. Doing what is expected merits "Thank you" or maybe "Good job". Attempting to do the technique or exercise can get "good try" to "excellent". Humans, particularly children, typically want attention. If you don't give them love and positive attention, they will likely seek negative attention.

Reward behavior you want. Ignore behavior you don't want and redirect without scolding or punishment into behavior you want.

For dangerous/abusive bad behavior, intervene and redirect quickly. If needed, explain why the behavior is dangerous or wrong, but explain what you WANT them to do INSTEAD. "Stand here when waiting your turn to avoid getting injured" is more effective than "DON'T LIE ON THE FLOOR!". Show that you are completely aware of the mat (you are a martial artist after all) so they are less likely to think you aren't watching them and can do what they want.

Adult helpers (15+ years old ) can be really valuable at keeping everyone safe and on task. A ratio of 1 helper to 4 to 6 children is very helpful. They need to understand the rules outlined above for handling behavioral issues.