My Chihuahua Jack Russell had 5 puppies 3 days ago and now they are full of fleas, what is the safest way to d-flea these puppies?

You need to call your vet and see what he recommends for pups so young, you cannot put chemicals on them.
The safest thing for them is to get a bowl of soapy water and remove the fleas with a flea comb and drown them.
You should treat mom, please don't go buy anything from the pet store or department store, some are toxic and yet remain available for the unsuspecting public to use, I don't get that, but it's true. Ask the vet for a safe product that he recommends.
You will also need to clean their environment, wash all bedding or throw it out completely and get new.
Vacuum the area they are in daily.
Fleas are very dangerous to such small pups (any pup-but I'm sure these guys are tiny)
They suck the blood, leaving them anemic, weak and can result in death.
So time is of the essence, you will have to be diligent or the fleas run amuck.

Octagon soap and Unscented Joy detergents are registered with the State of California as insecticidal soaps and safe for newborns, PROVIDING YOU KEEP THEM WARM. Dawn detergent is not listed as safe for newborns due to coloring and fragrances.

LadySam is correct about treating the mother and the environment. It will take a lot of work at least twice a day.

I certainly don't doubt what has been said about these products being safe, but quite simply these are very young pups and I would probably not bathe them until they have been looked at by a vet.
Although these products may be deemed safe for newborns, it is important to establish the overall health of the pups. While strong, healthy puppies could probably withstand a bath, as long as it is done properly, and pups are kept warm and dried thoroughly. In a heavier infestation where some anemia may already be an issue the stress of a bath could be dangerous and deadly. Since we can't see the pups, it is my suggestion to manually remove the fleas and do away with them.