Cat owners are all familiar with cat litter, and should be quite familiar with it. Cat litter is what cats use to urinate and is usually placed in the cat's litter box. This type of cat litter is for use, not for cats to eat. If a cat eats cat litter, it is a very harmful thing for the cat, not only affecting its health, but also potentially costing it its life. 
It's not a good thing for cats to eat cat litter, and you should stop it immediately if it happens. If your cat has already eaten cat litter, take it to the vet as soon as possible to check its abdomen and digestive system. If necessary, colonic irrigation or gastric lavage may be required.
Eating cat litter can be extremely harmful to cats. As owners, you should train your kittens from a young age not to eat cat litter indiscriminately. Feed them healthy food regularly and in measured amounts every day to help them develop good living habits and prevent any harm that could endanger their lives.