I wait for the pups to be over 3 weeks, usually 4 weeks. The pup's temperature does not reach the adult temperature until around then, and they cannot sustain a fever. So any type of illness, not just those we vaccinate against, can cause serious problems and death for puppies. Once they are 100 degrees or so, a fever that will kill an ordinary virus can be sustained by the puppy and they are a lot less susceptible to anything that might come from having visitors handling them.
After four weeks, I still do not allow strange dogs on the place, but I do allow people to come and see their puppy if they choose to do so. I also bring in my nieces to expose the pups to babies and children. Neither set of girls have dogs at home, so they can come in right at three weeks or just under. Usually before three weeks it really doesn't do much for the puppies. From 3-8 weeks having them around children and babies is very good for them.
Bear Cub, Hepsi-Pepsi
Cujo2, Karma Chameleon
Ramona the Pest, Kojak -- who loves you baby?
Tiny Tinnie, Susie's Uzzi, Kaiah -- The Baby Monster.