Congratulations!
A word to the wise about "little guys" from a breeder who knows how these things happen. If you want a smaller dog, then the smallest in the litter at 8 weeks when they're ready to go home, may not be the 'smallest'. The smallest is most likely the puppy that had lowest total % weight gain since birth.
Here's how it happens :)
Bitches are often bred 2-3 times over as much as a 5-7 day period. Even if they're only bred once, the semen can survive in utero for 72 hours before implantation. Gestation is 63 days. So ... a puppy that was conceived on the first day of breeding and a puppy that was conceived on the last of breeding could be as much as 1 week difference in development. With a gestation of only 8 weeks (give or take), 1 week is 1/8 of their total pre-natal development which is a LOT. When the oldest (first conceived) pup is ready to be born, he'll be born and all the others have no choice but to follow suit.
So that "runt" of the litter often times ends up not being the runt, he's just a week behind the rest of them.
If the breeder has been diligent about checking weights throughout the developmental stage, she will know which puppy is gaining faster and slower. That puppy that was born 1/2 the size of his sib's but is now almost as big as his sibs at 8 weeks has a good chance of ending up being BIGGER than his sibs. Likewise, the biggest born if no longer the biggest at 8 weeks will likely end up being smaller than his sibs.
So if your dead set on a small adult, ask the breeder about weight gain percentage.
5 days (now) is too early to tell, although she might have an inkling of an idea especially if there was a tiny one (big ones that slow down in weight gain take longer to 'tell'). She'll have a much better idea at 8 weeks when they're ready to go home.
Good luck and congratulations!!