Big size difference in 5 week old chicks. Should I worry?

We think these are either silkie or Orpington, as those are the only types the breeder has. They hatched from two white eggs, and one brown egg. The breeder told us the brown was Orpington. So the brown chick and the runt are both supposed to be silkie but look very different in feathers and size. Should I be concerned about how small the smallest is?