Very young chat
The safest way to treat a puppy under 6 weeks of age for fleas is to bathe him using warm water and Dawn dishwashing detergent and then to manually pick off remaining fleas. (Test the temperature as if you were giving a baby a bath). Massage the soap all over his body and around his neck, ears, face, head and under his chin, being very careful not to get soap in his eyes.
Dawn dishwashing soap is very effective and it kills fleas quickly. Using the kitchen sink is often easiest as you don't have to bend down and you are more in control. The fleas are not silly and will head for the high dry ground of the head area. If he is not fighting and struggling too much try to keep his body submerged (with his head above the water of course) for a few minutes.
It wouldn't make a lot of sense to get rid of the fleas on a puppy then put him back with his mother who is infested with fleas so you should first treat the mother dog.
You should treat her with a top spot flea treatment such as Advantage, Frontline or Revolution.
One to hold the puppy and one to massage and wash the the puppy.
When finished wrap him up in a dry towel and dry him off.
While the puppy is still damp comb over his body with a flea comb or pick off the remaining live fleas with you finger and thumb nails while they are struggling to get through the damp hair.
The makers of top spot products recommend that you apply them monthly but I have found that once you attain flea control in your surroundings you may not have to apply the top spot for many months.Many people ask this question and so often they are given the wrong advice.People will often recommend flea powders, flea rinses, flea collars, essential oils and other chemicals that are far too dangerous to use on puppies less than 6 weeks old.Immerse the puppy up to his neck and insure that he is saturated. If he is distressed get the job over and done as quickly as possible.Having two people perform the operation is often easier.