Why is your older cat licking your kittens butt?

Absolutely. The way that most intestinal parasites are transmitted is through the feces. I suggest deworming both the cats. But first, you should take the cats to your veterinarian. Your vet will perform a test on the feces to see what kinds of worms the cats have. The reason you need to know what kinds of worms they are is because there is not one dewormer that can kill all types of worms. Sidenote: An animal may have worms but it is possible that you will never see the worms in the stool. The reason is that the worms live in the gut and never leave it, the only thing that comes out in the poop is the microscopic eggs. There is only one type of worm egg that is visible to the naked eye (tapeworms). Ditto! Both the older cat and the kitten need a trip to the Vet. They need to be tested for all the different worms and then be dewormed. If one has worms it can have other things as well, so best to get a general check up on both, just to clear them up for all the little nasty bugs and viruses creeping about. Vet Trip ASAP!