Have them shower and pee before getting in the pool and see if it helps

I see the same thing if I have LOTS of kids in the pool.

I think the bather load uses up the FC, and vigorous activity tends to suspend air bubbles in the pool. A little extra FC might help hold off the cloudiness, and a shot of bleach after the swimmers are done might clear it up quicker

I don't think adding CYA will help the cloudiness, but a little bit more might reduce your chlorine costs a little.