That looks like a mild case of dry pox. As long as they're eating and drinking they should be fine. If you see any that look off, or aren't eating, give them a thorough exam and check their entire body, including the insides of their mouth. Dry pox lesions can be found any place on the body without feathers. The comb is more common, but they can also get them on their legs, feet and vent. Wet pox lesions are found inside the mouth.