At 6 weeks old, to be safe, I would start them on Corid as soon as possible. I do see what appears to be some intestinal shed in some of the droppings, and maybe some mucous. Some of them look like cecal droppings, which could be normal, but the fluffed feathers and lethargy make it concerning. Coccidiosis can take them down fast, depending on the strain, and treating quickly is the best chance for full recovery. Corid is very safe, it's not an antibiotic (it's a coccidiostat) You can get it at most feed stores and tractor supply stores, etc. Most people find the liquid to be more convenient, but either will work (Images below).
Dosing is 2 tsp of the liquid or 1 1/2 tsp of the powder mixed in a gallon of drinking water. The medicated water should be the only water they have access to during treatment, no puddles, ponds, etc.
Treat for 5 - 7 days, make a fresh batch daily. Treat all of them kept together. For those showing symptoms or not eating or drinking normally, you can give an oral dose once a day as well as the medicated water, dosing instructions for that is by weight and is here:
https://www.backyardchickens.com/threads/corid-oral-drench-instructions.1211991/
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