If they have leg mites, the scales on their feet will look like they're lifted up. How much lift depends on how bad the infestation is. Get vaseline and smear it really thick on all their legs. Its important to put it on really thick, you want to kill the mites. I would do this every couple days for 2 weeks just to make sure you killed them. I would also give them a big dust bathing box with DE in it. That way if they have body mites, they can treat themsves. A dust bath is very important for a chickens health.