There are a few products your vet can prescribe for nursing pups. Those are your best bet, very effective and inexpensive. In the mean time you can bathe your b!tch and pups in Dawn dish soap. Make sure to keep the puppies warm at all times, it's very important they don't catch a chill.

Go to your vet and get a flea product that is safe. Please do not go to the pet store or grocery store and pick up any type of flea medication (especially Zodiac, or Hartz).
Revolution is generally the best all-around flea product, and is safe to use on nursing mothers.
In the meantime, follow Aurora's instructions. If the pups are really really young, wet a flea comb and manually pick the fleas off several times a day instead of bathing them.

No flea collars for the mom, either.