Barred Rock chicken size

This is my first year with chickens—four barred rock pullets.  I’m anxious for home grown eggs plus the nitrogen enriching manure for my compost pile!

They chicks are almost 2 months old.  One of the chicks is about half the size of the other three.  They all hatched at the same time and have been kept in the same brooder.  The comb and feathers are coming in just a tad slower than the other chicks. 

Is this something I should worry about?  Or, is this just a normal generic variation?

Thanks!

-Eric

More upright walk?  Taller but thinner ?  Could be a rooster.

No, not taller...  just half the size... I took a couple of pictures--maybe this will help!

Thanks!

-Eric