choosing shih tzu puppy

Question
My family had to put our 14-yo Shih Tzu to sleep in Feb and are now looking for a puppy.  Our dog had been 10 lbs. The parents of the puppies we're seeing now are 14 to 18 lbs.  How predictable is size compared to the parents?  One puppy we are looking at is the runt of the litter.  Would she likely stay smaller?  Also, this particular puppy's mother has thinner, wiry hair.  Would we be able to tell at 6 weeks if the puppy's hair would be the same? I hate to be so picky.  We just thought our last dog was perfect!  Thanks for your help!

Answer
You can usually tell by the parents and grandparents what your pup has a chance at turning out to be.  The runt does not always remain the runt (a lot of times the runt catches up or outgrows the litter).  If you want a puppy that is 10 lbs at maturity you need to find parents that are 8-12 pounds.