Sherril the only thing you can safely do is buy a fine toothed flea comb. Take a small empty jar, fill it with hot water and a few drops of Dawn liquid detergent, comb the babies out and drop the comb in the water- wipe the comb off good, comb the next baby so on and so forth. Do mom last.
Fleas can come into you home on your shoes, on your clothes, or even just through an open door. You let your cats outside, and the fleas can jump on them and travel back indoors that way. You can flea treat your other cats with Advantage or Frontline, BUT not the nursing mom, too dangerous with all her kittens around her and nursing off her.