They do appear to be going through one of their multiple baby molts. Have you observed them for feather picking? It's something that comes to mind based on where they are missing feathers. I have a couple of lavender Orpington chicks 3-4 weeks old and their feathers look strong, I had read about the problem that comes with the color, but so far mine look fine.
I will definitely give that a try. I've been giving them an organicThey do look under sized based on the size of the eyes relative to the head, but maybe that's because they are missing their muffs. I find scrambled eggs given daily is a wonderful protein boost and makes them grow quickly. It does give them stinky poop, but the reward is worth it to me. Hopefully with correct feed they should straighten out. Otherwise they appear healthy in the photos except the feathers.
That's the general amount of protein in a starter grower. You can find something with more, but that should be fine, especially if you sneak a bit of egg in their diet.Sorry... my kids.... I've been giving an organic starter/Grower feed with 18% protein. Does that sound appropriate?
I agree with @oldhenlikesdogs . Your birds look fine. I don't see any disease at all. I raise several varieties of Orpingtons as well as FBCM, and sometimes chicks can look wretched when they lose their down and before all their sets of feathers come in. Also, sometimes there is late feathering with the black gene (lav is a recessive black gene). Since feathers are basically protein, increase your chicks consumption of protein, and that may help. The suggestion of scrambled eggs is a good one. Mealworms and cat-food kibble are other easy sources of protein that chicks love.other than ugly feathers does anything about this bird look sick to you?