First take that bag and dump it where they can't find it.
Did any of them not get the medicated feed? I know it is unlikely but with all your broodies and chicks, one can hope. If some did not get it, find a way to feed some of their poop to the others. Animals eating each others poop is a way to share probiotics. Some baby animals eat their mother's poop to get the right bugs in their guts.
Do not get other strange chickens' poop and feed it to them. That is a good way to spread parasites. But since yours free range, they were sharing poop anyway. It won't hurt them.
Did any of them not get the medicated feed? I know it is unlikely but with all your broodies and chicks, one can hope. If some did not get it, find a way to feed some of their poop to the others. Animals eating each others poop is a way to share probiotics. Some baby animals eat their mother's poop to get the right bugs in their guts.
Do not get other strange chickens' poop and feed it to them. That is a good way to spread parasites. But since yours free range, they were sharing poop anyway. It won't hurt them.