There are a couple of things that work great on a kitten that age. The first is Adams Flea Off Mist and you can get it from most pet shops, feed stores, vets and even Wal-Mart. It kills them on contact and is safe. The other are products that come from your vet and use them once a month. One is Advantage and the other is Frontline. You apply it on the back of the neck once a month You can even us the Adams with either of the others if you need to but not on the same day. Sometimes in between the months you may see a flea or so and you can spritz some Adams on them. Adams is 100% safe as we have used it at the clinic where I worked for over 20 years on kittens just a few days old ( by applying it with a cotton ball) and then washed it off of them with plain water. Fleas will kill your kitten if they suck its blood until it is anemic. Take a look at this link about the safety and use in young pets.

http://www.shopping.com/xPR-Adams_Flea_Tick_Mist_23697260~RD-838098

There is a pill called Capstar that can be used also which is given once and rids the kitten of whatever fleas are on it at the time. It can be gotten from your vet.