I have two brooders working right now, one in the Nursery/Bathroom with six chicks, 3 are 6 days old and the other three are 4 days old. The "older" chicks are bantam cochins and about a third the size of the younger, Orpingtons. (Not sure if the Orps are blacks or blues yet.) The other brooder has 7 chicks, 5 olive eggers about 6 weeks old and a BJG and LB about 5 weeks old - this brooder is on my covered back porch.
The Nursery brooder chick dynamics are hysterically cute to watch. Those itty-bitty bantam cochins have rank over the much larger orps.
The Porch Brooder chick dynamics are much more straight forward: older, olive egger cockerel with the largest comb pulls rank on ALL the other chicks. The LB appears to be higher in the pecking order than the BJG, although both are pullets and the BJG is bigger than the LB.
Interesting.