[Siskin]

Unless you bought your pup from a KC registered breeder who is active in showing their dogs, therefore more likely to have dogs that adhere to the breed standard, your pups eventual size could be anything. If you look around at the many staffies about you will see a huge range of sizes from quite small ones to tall leggy individuals, more often or not they will not be pure bred staffs and this could be the case with your pup. Or, as Muttly has said, he could just be a small puppy.
He looks well, bright eyed and does look round about 9 weeks. So long as he is eating well, active, not pot bellied (which could indicate worms) and weeing and poohing normally then I shouldn't worry. Has he been to see a vet yet? What did the vet think?

 

[Siskin]

I've seen both parents and they both look pure staffy, which is what the breeder told me too. We did see his brother and sister who were both a lot smaller. I know he was nipping his mum before we picked him up so he was weaned a bit early. He has been wormed and he doesn't seem to have worms. He eats fine. My dad was saying that he walks like a baby though. That's what got me worried!

What do you mean by 'nipping his mum, so he was weaned a bit early'. I'm not at all sure one thing means the other

 

[Siskin]

This is our Staffy pup with her siblings and Mum, taken when the litter were eight weeks old.
View attachment 296897

What a fabulous picture