I found this recipe via Pinterest - apparently you can use orange liquid as a spray - it might be worth thinking about if it's ok for kittens etc:
Homemade flea spray: Put the peels from three or four oranges in a large saucepan with one quart of water and boil until the peels are soft. Let the peels cool, then blend the peels with some of the cooled water in the blender. Return the blended peels to the rest of the water, then strain and funnel the strained liquid into a spray bottle. This mixture can also be sprayed on pets, furniture, bedding, carpets, this actually kill the fleas.
I've not tried it myself and I would check with your vet to see if the citrus are ok for kitty to digest when they lick their coats.