Breed?

I am new to backyard chickens. I have five, four are five weeks and one is about three weeks. I got the brown chick and gold chick from the same bin labeled "English Orpington," but the brown chick doesn't seem to be an Orpington. She's smaller than her golden sister, and her coloring is different. What breed do you think she is? I included a couple photos of the golden chick for comparison.