- A female kitten's genitals will resemble an upside-down exclamation point with the vertical vaginal slit below the anus.
- A male kitten's organ will look more like a colon with the penis below the anus separated by a space to accomodate his testicles. You may even be able to see very small lumps in that space, which will grow into testicles as the kitten matures. Because of this space, the female's vaginal opening is closer to the anus than the male's budding penis.
It will be very difficult to accurately tell the sex of a kitten until it is at least two weeks old, and even then, both experienced breeders and veterinarians have been known to make mistakes. An excellent video by the About.com video team shows a veterinarian demonstrating the differences between male and female cats, using live cats.
I feel compelled to remind you before closing to be sure to spay your mother cat as soon as the kittens are weaned. Also, make sure the kittens are all spayed or neutered before releasing them to other homes. Kittens can be safely neutered as early as six weeks, and doing so will help prevent another "oops" litter. You'll want to keep the kittens with their mother for 12 weeks if possible, and at a very minimum of eight weeks. They need this time with her to become fully socialized, both with other cats and with humans.