My pups have never had worms either. I also feel very blessed about that. I think your Mamma dog would have to have worms....there really isn't another way for your pups to get them unless they are around other animals (which they shouldn't be at that age). I'd give the vet a call and ask him how your pups could have worms if the mother doesn't. I can imagine how freaked out you were
! I'd freak too! Hope your pups are all healthy and you never enounter another worm
.
P.S. Keep their area very clean and don't take them outside yet.