Mother cats might eat their kittens’ poop for the first three weeks of their kittens’ lives during anogenital stimulation which is a form of tactile stimulation by the mother to encourage her kittens to urinate and defecate. When she does this she might eat their poop. In other words she might cleanup. It’s important, I think, to realise that if a mother does eat her kittens’ poop is as a side effect of anogenital stimulation. For completeness, the word “anogenital” means “relating to the anus and genitals”.
There is nothing more to say on that specific topic in answering the question in the title. I will, though, add a few more words. Common sense dictates that if kitten poop is present in the nest it should be removed by their human caretaker if there is one.
Some links selected at random to more kitten info
Video of Martin Stucki taking on the role of a mother cat in carrying out anogenital stimulation of Savannah cats and feeding them
Some more on early kitten developement
At birth, kittens’ ear canals are blocked by ridges of skin. These ridges gradually open over the first two weeks of life. When they are as young as five days old they startle at loud noises. At two weeks of age they are able to locate sounds in their environment. By four weeks of age their sound detection and reaction is adult-like. Their deciduous teeth first erupt at two weeks of age and continue until week five. This is about the time when their mother, if she is free-living, brings home killed prey as solid food for her kittens. Transitioning from deciduous to adult teeth begins at 3.5 months after birth.
Kittens’ neonatal behaviour slowly disappears and is replaced by adolescent and adult behaviour patterns after three weeks of age. Kittens become more mobile between 9 and 14 days which ties in with the development of their auditory system, and the opening of their eyes. They can run at about four weeks of age and their play patterns become more complex during weeks 7-8. At seven weeks old they have a full adult repertoire of locomotion.
My grateful thanks to Linda P Case’s book: The Cat, Its Behavior, Nutrition & Health (pages 118-119). I also referenced the internet at various websites to see what less experienced people said aabout this topic.