Why are my 2.5 week old chicks having diarrhea?

[SteeleyAcres]

I also have a brown hen that seems to have some stool in her fluffy area below on her bottom. What do I do about that??

Im not experienced with chicken I just purchased my first flock. But I did hear in the warmer seasons it's important to keep your chickens butt's clean otherwise you run the potential risk of them getting "flystrike." Flys are attracted to poop and will lay their eggs in it and then the eggs will hatch and the maggots will eat your live chicken from the inside out. Flystrike is curable if you catch it early enough. You have to remove the maggots and treat the wound. Supplement antibiotics soak them in an Epson salt bath and keep the wound clean. There is usually more than one round of maggots that will hatch usually a day or 2 apart. Monitor the chicken for about a week once a scab forms you should be good to reintroduce your chickens to the hen house at night.