I have personally played two different catfolk females (I love cats. what can i say?)... GMed two campaigns containing both Catfolk and elves And over the YEARS I've introduced a boatload of nonhuman NPC into games... And when you actually STOP and think this topic through to the logical conclusion it becomes a bit self-explanatory
Elves, and Dwarves: Both of these races are much LONGER lived than humans and yet both are supposedly rarer than humans. Which at FIRST would seem to be counter-intuitive. IF a matted pair of elves, or dwarves, is capable of one offspring every... 10 to 12 months for any real percentage of there lifespan? The elves should be overrunning your game world… and they aren't. And neither are the Dwarves, nor the Hobbits. So the answer must be one of the two elements above. Either elves have a vary narrow window of fertility. (Say 12ish years following puberty?) Or go for extended periods between fertility cycles (A child once every two to three hundreds of years?) The only alternative to this set of possibilities may be an incredibly high rate of infant mortality within the race (80 plus percent?). And when you think about this 3rd alternative, this has the potential to make elves the most tragic of all the races available for the PCs
Hobbits: Gandalf himself has offered up one possible answer in this case… that the hobbit population is slowly being melded into the human population of the game world, and will in only a few more generations be indistinguishable from the human population. For this to be the case MOST LIKELY means that human DNA contains more dominant genetics than dose the hobbit bloodline, and the interdiction of even a few samples of the more dormant will be more than adequate in the long run.
Catfolk: Catfolk have a noticeably shorter lifespan than do humans. And this fact dose undoubtedly account for a major element in the question of the rarity of the race within the game world. Yet even with the ability of a mated pare to only produce a ‘small’ litter of say 2 to 3 kits per mating cycle… the shorter lifespan should not be sufficient to keep the population of these creatures in check. My own explanation for this has normally been that A.) Catfolk enter in to puberty slightly latter in the life cycle than do humans (about 16 or 17 years of age) and shortly there after (either in the late summer or early fall of the indivigual’s18ish? year.) enter there first heat/matting rut. And I as the GM begin imposing penalties in both the PCs intelligence and wisdom, until either the PC capitulates, or for the entire week long window of fertility. IF the breading is successful a litter of two or three kits will be born about 10 moths latter. I personally say that CFs subsequent matting cycles are dependant on the levels of stress hormones and relate back to the kits already in the family so that a new matting cycle only begins when the stress of raising (Preteen?) offspring is lessened.
I know. I’m a total geek for having taken the time to think all of this out… and each GM needs to be able to add his or her own unexpected twists and turns to this topic just to keep the players guessing and on there toes. But if any of the above ideas work within your own campaign… Help yourself.