We have 9 3-week old chicks we got from my son's kindergarden class after they hatched. They were doing fine until today I noticed a few (4) of them have a very swelled belly (below the vent) and are not as active as the others. Their butts are clean (no pasty butt) and the are at the right temp for their age-85 degrees. They also are getting fresh food and water twice a day. The swelled area is affecting their walking and I don't know what to do for them. Thanks for any and all help.