You can bathe them using Original blue Dawn. Make sure the water is warm and the room you bathe them in is warm. Before placing the kitten in water, use a bit of Dawn and a bit of water to make a collar around the neck area only. This will help keep fleas from running onto the kitten's head and into ears, eyes and mouth. Also, dry them off very well and place them in a warm area for a bit to thoroughly dry.
I had a litter of four kittens last summer that had fleas from when they were two days old. We bathed them almost daily until they were two months old (when they were finally big enough to treat) to keep the fleas under control. We used dawn dish soap; definitely get the neck area wet and soapy first and don't wash their faces if you can help it. Wekept them in a small room with a space heater to keep it really warm for them. Also, change their bedding daily and wash it with hot water. If the mother cat is still with them you can treat her with a topical like frontline or advantage and that will help the kittens a little also.