Do you have a lot of flies around the litter box? Maggots would only be present if the flies are laying eggs on your cat's fresh stool.
Maggots can infest the skin of cats/dogs also. If there is a wound in the skin, or feces on the fur, the flies will lay eggs there, and the maggots can then start eating through the skin. It is very gross, and can kill an animal if not treated right away. If there is any afterbirth mess still on her fur, this can attract flies.
One thing that some people confuse with maggots are tapeworms. Tapeworms are small, white worms that you can see on fresh feces, and sometimes crawling around the fur around the anus. The tapeworms are smooth, while maggots have a more rough appearance. Tapeworms move slow, while maggots tend to move very fast. Tapeworms can be caught from the cat eating fleas, or also if they eat rodents or rabbits, which carry the tapeworms. The tapeworms will dry up, and then they look like small sesame seeds, and you can find these on the cats fur or on their bedding.
This website has a picture of the tapeworms in stool and the dried segments on the fur. They have a dog in the pictures, but they look the same in cats. http://www.thepetcenter.com/exa/worms.html Scroll down to the last section.
Do you think that it might be tapeworms you are seeing vs. maggots? Please reply to discuss further!
If you are seeing sesame seed type things, then I would have to suspect tapeworms. Fly eggs are small, white, and about the size of this apostrophe: ' . So, if you are seeing larger things you suspect are eggs, and they look like dark sesame seeds, these are probably dried up tapeworms.
However, if your cat and kittens are not clean, you can certainly get a maggot problem if there are flies around!!! THis is very dangerous to the kittens! Are you just finding these in the litter box?
One thing you can do is collect some of these things you suspect to be maggots in a baggie, and some of the eggs, and take them to a vet office. They can tell you if you have a tapeworm problem or a maggot/fly problem. We do this for free, but some vets do charge for an ID of a parasite. If there are tapeworms, your vet can dispense a medication to kill the worms. It will pass into the milk, but should not harm the kittens.
If you have a maggot problem, you need to examine all the kittens and your cat, and make sure they are all very clean. Give momma cat a good bath if needed to remove any afterbirth. Rinse her well so no soap is on her nipples. Change bedding once or twice daily. Keep the litter box scooped immediately. If you notice any maggots in the skin of your cat or kittens, this requires immediate vet attention.
Please reply if you have further questions.