well I have a yorkie mix... momma is a full bred toy poodle.. 4 pounds.. daddy is a yorkie poo mix... 4 pounds.... Tucker... is 9 pounds.. he is the same height has his daddy but obviously weighs a good deal more. I know that he is a mix.. but anything is possible. You cant always go buy what the parents wiegh. However a good breeder would have a record of what past pups wieghed, for generations so a decent breeder could give you a estimate of what the pup may wiegh, but nothing is guarenteed..
oh and ive seen both parents on a regular basis... they are still both 4 pounds..