Totally normal and to be expected. It would be very strange if they are not all doing that. There are a lot of partially digested nutrients concentrated in there, plus that is how they develop flock immunities and share probiotics. They are going to do it no matter what you do.
The danger is if they are in a wet brooder, coop, or run. Certain dangerous microbes thrive in wet poopy soil or bedding. It can be really hard to keep a run of any size dry when the weather sets in wet. Usually that is not a huge problem if they have dry places to go, but a wet brooder or coop is bad. As long as the poop doesn’t stay wet for a couple of days so that microbe can develop, them eating each other’s poop is not a problem. I consider it a good thing so they can share probiotics and develop flock immunities.
