
Average weight for my breed who are 43 -50 pound as adults is 10 0 12oz, and I have fairly frequently had them at about 15pz. I would think your freinds pups are most untypical.
I have often seen poorly bred cavaliers the size and look of Welsh Springers. I hear that puppy farmers often cross the cavaliers who don't ahve bitg litters with a Springer to get the num bers, as most of the Pet buyers who buy from such sources would be none the wiser.
Whelp size is very interesting. On that really surprised me is how small Giant Sznauzer pups are listed as being ion the book of the bitch, as they can be quite tiny considering what they grow into.