Have you ever seen a litter of kittens that are all different colors, some long-haired , some short-haired and maybe even one that looks like a Siamese mixed in there too? If you think it is unlikely they were all from the same father, you are probably right!
The Heat Cycle
Female cats are seasonally polyestrous, which means they can come into heat several times a year, often during spring and summer, and they will cycle multiple times if they are not bred. During the first stage of heat the female will vocalize and often roll around on the ground and rub up against objects -- this behavior can be quite annoying to her humans! At first she will reject advances from tom cats. Later in the cycle she will allow a tom to approach her and mate.
The male cat will usually grasp the back of the neck of the female with his teeth as he mounts her. Feline mating is quick -- usually lasting only a few seconds. Male cats have small barbs on their penis which rake the vaginal walls as he withdraws from her. At this point, kitty will likely scream or howl and swat him away with her paws. After that she will calmly groom herself and want to be left alone for an hour or so.
Female felines do not release eggs from their ovaries until stimulated by the mating process. This is called induced ovulation and usually occurs from 20 to 50 hours after mating. Miss Kitty s likely to breed several times, and with different tom cats, before her body tells her ovulation has begun. This is why her kittens can have different dads -- there can be sperm from several different males in her reproductive tract as the eggs are fertilized.
The term for two or more eggs from the same heat cycle being fertilized by different sets of sperm is called superfecundation. It is not unique to cats, but is also common in dogs. Although not likely, it is theoretically possible for every single member of a litter to have a different father. Though extremely rare, it is even possible in human twins!