Slightly droopy eyes??
Featured Stories on BackYard Chickens
If they are eating poorly, have runny droppings, or are hunched, coccidiosis might be a problem. It's common when chicks of different ages are together. Corid or amprollium is the treatment in the water for 5 days. I would be cautious putting young chicks together with older hens without a fence between them. The young ones can be injured.
My adults are bantams, so I figured since the 6 week olds are the same size as the adults, it was a safe bet to put them together now.