If they don't have 5 toes then it is definitely not a Silkie and as Timily Farmas said they have darker feet and beaks, I would say it was either a Partridge Cochin or a Partridge Brahma because of the feathered feet.
Could it be a mixed Silkie? I'm reading about other people who had chicks born with lighter feet that got darker and born with 4 toes instead of 5, and they all say it's a mutation or mixed.
They look like Partridge Cochin chicks. They might be mixed but its probably more likely the people at the store didn't know what they were talking about.
So I called the store, politely asking what they might be if they aren't Silkies.
I got a manager, and she was rather upset with her employees for telling me they were Silkies, because they don't know what they are. She said they come in a box that says assorted bantams and that's all they know about them. They don't even have a list of possibilities. I'm hoping for the Cochin, I think they're prettier than Brahmas.