Older cats hate new kitten?

I found a stray, sick little kitten the other day. We took him to the vet, took care of his fleas and cold, and now he is a wild, crazy little guy. My two older females (one 15 and the other 5) are terrified of him. When he gets near, they growl and hiss. The five year old, Opal, is my cat, and won't even let me hold her without growling since I smell like the kitten. Toulouse (the kitten) was being totally playful with them- running up to them, trying to snuggle, and the like. I know its annoying to the older cats- but they didn't act annoyed, they acted afraid. Now, when Toulouse gets near them, they hiss and growl and back away, and Toulouse is starting to do the same. I don't want any aggression- what can I do to prevent this?