Some flea products can be used in kittens as young as 4 weeks. For kittens younger than 4 weeks, groom with a flea comb, or pick fleas off with a tweezers. Be sure to keep the kittens warm while you're working with them; wash their bedding; and vacuum the surroundings.
Fleas can remove enough blood to make kittens anemic, so confirm that the gums are pink. Because fleas carry tapeworms, watch for rice-like dried tapeworm segments at the rectum or in the stool over the next several weeks.
For kittens with biting (adult) fleas, you will likely want a product that works quickly to kill these parasites. Capstar is a popular flea product that works within 6 hours to kill 90% of fleas. Once adult fleas are removed, it's important to also kill flea offspring (flea eggs and larvae) to prevent reinfestations. Products that affect flea offspring are called insect growth regulators (IGRs). IGRs are very effective when you can clean up the environment and the kitten will have little exposure to fleas in the future, either from the environment or from other animals-such as our indoor cats.