I have a bull terrier pup that was supposed to be born on 12-20-04. She was 2.2 lbs when she shipped on 2-13. Ears were flopped over and she didnt respond to noise....we thought she was deaf at first, but now I am thinking that she just was so young they werent open.
She is 4 lbs now. Her ears are up. She hears FINE (when she wants to..hehe)
It's hard to tell at any age if the puppy is a runt or just small. Some dogs that are "tinies" or "runts" of the litter grow up to be over the standards, or just perfect. Keep an eye on your dog, you'll know.