My cat had the same thing, and thought it was from the kitten. It turned out it was from the fleas. She was horribly allergic to them and was scratching herself really hard, and often in places that looked like there was no way she could've reached herself. The vet called it Flea Allergy Dermatitis and gave me a spray called Betagen for the scabs. It didn't really help.
You must get rid of the fleas. Skip any over the counter stuff - it doesn't work and is very toxic. Go to your vet and get Frontline or Advantage. Wash everything in your house! Vaccum thouroughly and get rid of the bag right away. Sprinkle borax in your carpets and furniture. It kills fleas but is non-toxic. If you can, bathe your cats. Fleas drown, so any good lathering cat shampoo will help. Use a flea comb. For my scabby cat, I used a shampoo called Septiderm-V that really helped a lot.
Also, you may want to get a tapeworm pill from your vet. Fleas carry tapeworm. I didn't notice that my cats had tapeworm for a long time, but they did. Good luck.