Hi
It's difficult to make out from the photos but it looks like pin feathers coming in which would suggest it's just a juvenile moult. Is the skin actually broken or is it just feather damage/loss, which is what it looks like in the photo?
Do you only have 2 chicks and no other poultry? Two is not a good number because if you lose one you end up with a lone chick or hen and finding a companion of a similar age can be difficult. 3 or 4 is much better.
Mites live in the coop and crawl onto the chickens at night to suck their blood. They can cause anaemia and pass on infections but they don't usually cause feather loss. Lice live and breed on the chickens and whilst they don't pose a health risk as such, they do cause irritation and can lead to the chickens over preening. Ensuring that chickens and chicks have access to a dust bathing area is an important part of chicken management, so that they can keep themselves clear of these pests.
The best way to assess a problem like this is to spend time just observing them and see how they are behaving. If it is feather picking, usually lack of space and boredom are the key factors.
I hope that has given you some ideas to look out for and/or hopefully put your mind at rest.
Best wishes
Barbara