Hi,
My sister has a resident cat (9 months old) and two small kittens (about 10 weeks old). The kittens are from the same farm as the older cat. She has been careful to introduce the kittens slowly, and the cat seems to warily tolerate one of the kittens. However, the cat seems to hate the other kitten. The kitten the cat targets is the 'runt' of the litter and looks tiny and run down (she has had the all clear from the vet). Could this be why the older cat dislikes her so much? I have seen cats who dislike kittens, but I have never known them actively attack them.