Buy a copy or go rent one from the library of "the chicken health handbook." Observe what kind of droppings they are having. There is a chicken droppings chart out there on the internet, that might even be from the chicken chick too. See what's normal and what's not, then treat from there on what you think it might be. Are they on medicated starter? They could have coccidiosis (mostly observed by their droppings, seen as blood in stool, diarrhea, etc). Coccidiosis can weaken the immune system then they can get something like a cold easier. You can tell a lot from their droppings. Also, in the back of that chicken health book there are extension numbers you can call in your county, this may be useful. You could also contact who you bought then from and explain what is happening. Hopefully if they are dealing with something too, they will tell you. Never by anything that looks like a sick chick or bad living conditions. I learned this one the hard way at our last house. The hens all fit aggressive and started picking away at each other, after sneezing and being wheezy. Thank goodness the owner took them back (they were her babies so she happily took them back).