Can openly declare his desire. But it is not very reliable. Usually, after several such statements by the parents refuse to speak on this subject.
Or cat friends to show parents how you can be a caring owner. Pretty good method, but it doesn't work 100%.
To tell about the usefulness of cats. They rid the mice treat the disease, those who have the house has a cat, lucky, and never depressed. This method is not quite suitable for those, whose parents once had a cat.
To put pressure on pity, but we need to do this carefully so as not to overdo it. Tell about cruelty to animals, homeless cats, based on a specific case, to start like that recently saw a stray cat or kittens in the store, such sad eyes. Some parents can resealability and allowed to take or even to buy a kitten.
You can "play" in the fan of cats. To watch on TV programs about cats, cartoon cats, read books, stories, buy stickers, toys, trinkets with cats, and at any mention of cats, start admiringly, tell me about them. Thus it is necessary to know about it parents. So they will make sure you really like cats and be a good host and her kitten.