How exciting for you.....I'm sure you can't wait.     
Most puppies are just being weaned at 8 weeks old, and require more time with mom....Mom has so much more work to do than just feeding them.  Socialization being one of the jobs.  The recommended time for a breeder to allow a puppy to go home is 12 weeks of age or longer. 
When transitioning to a new home and new environment they tend to not eat well for a period of time.  So, these wee ones should be on a solid food and eating well before they leave the breeders home.  In addition they should have a minimum of 2 vaccines, which begin at approximately 8-9 weeks..... 
The breeder should make sure that every precaution is taken to make sure that the puppy's transition is as smooth as possible.     
				__________________  Mardelin  Yorkshire Terriers      |