This little Serama looks a week or two younger than it's siblings and has delayed feather development compared to them. They are all 3 weeks old, and all them including the runty one are eating and drinking fine. The two mother hens seem to be preferring the runty chick over the others as well, kicking the larger ones out of the way so the little one can get their fill first.
Here it is compared to a sibling of the same colour.
Here it is compared to a sibling of the same colour.