If it was a 2 week camp, it actually sounds like a good idea. Just keep them there a bit longer maybe.All of those age groups have less chance of dying than the flu.
Whoever brought it to camp, didnt give it to an older population.
eta:
the studies I have seen have very low transmission below 10 years old.
That would only work if everyone was sick on day 1. In real life some infected people would past it in to uninflected people over time, resetting the infectious window. Some campers will first be experiencing the infection just as they are being let out of camp.
Death is not the only serious risk. And I doubt many parents would feel assured “Well the chance of dying is less than that of the flu.” I would not send my kid to a camp if there was a siginificant chance of them catching the flu.
The transmission issue has been addressed upthread.