It is normal for many animals to eat poop, their own and the poop of different animals. There are a lot of undigested nutrients in some poop and a lot of microbes, some of which are very handy to the health of the chicks. In the flock when raised with their mothers, chicks eat the adult poop to get microbes so they can develop immunities from some of the parasites and such that the flock has. Chickens really love working over cow poop. They fine a lot of bugs and grain in there. I saw a Discover Channel show where a baby elephant eats its mothers poop to get the right microbes in its stomach so it can digest adult food.
It is not gross to them. It is necessary to their health. Welcome to the world of animals.