"Torture the Teacher"
They, one at a time or in a group, do reps of an exercise. The coach will then do all the combined reps in one set or set per set. My kids loved it, especially whenever one kid would finish and I might finally fail or barely eek it out. It goes faster if you match them set per set (and it gives you breaks).
It's all about the kids vs the coaches rather than pitting them against each other. The kids know who is stronger than each other except for those kids who might be stronger in one regard than another or are tied.
Just be mindful of what kind of exercises you use. Like squat jumps, don't do squat jumps. I did once and didn't walk right for 2 weeks.
I also like the circle up and we either substitute the number of letters in a kid's age for repetition numbers or the day of the month (5, or 17, etc). This is good for circle conditioning as a group when you don't want to spread out amongst the apparatus.