Feathers

Chickens don't molt until their 2nd autumn so at 8 weeks it isn't that. Do you have any birds that are perhaps picking the others??

 

Could you post some photos of your chicks? Chickens grow in 3 sets of feathers before they reach their adult plumage. During the time in which they are growing in new sets of feathers, they can often have bald patches on their skin and you will see a lot of feathers lying around. This replacing of young feathers and growing in of adult feathers is not generally considered a complete molt (chickens go through those when they are about a year of age), but it is still a type of molt.

If it is not a simple replacing of feathers, then I would suspect that your chicks have mites, or you have a chick or two that are bullying the others. To check for mites/lice, look near the vent, under the wings, under the neck feathers, and near the tail for any small black moving specks (mites) or larger yellow blobs (lice). Observe your chicks for 30 minutes or so for any bullying and feather pulling.