Having owned cats most of my life, and battled with various problems trying to keep fleas under control, I have experimented with EVERYTHING poeple have suggested to me.
I don't much like to use strong pesticides around animals anyhow, and you can't put flea collars on young kittens, so this is the best thing I have found as an alternative:
Eucalyptus
If you live in an area that has eucalyptus trees growing, you're in luck! Go out and gather some leaves and some of the little nuts that they drop. Crush some of the leaves a little, and
put them and some of the little nuts in strategic places around your home (ie behind furniture). Save the rest in a ziploc baggie so they will retain as much of their scent as possible.
Fleas will leave your home. If they come in on your pets, they'll leave because of the eucalyptus. They can't stand it!
Some eucalyptus oil rubbed into your pets' fur helps them, too!