Essential fatty acids (like omega 3 and omega 6 fatty acids) and fat soluble vitamins (Vitamin A, Vitamin E, Vitamin, D, Vitamin K). The plain fat is a nutrient too.
Kittens, generally, can begin to use a litter box at about four weeks of age, and a kitten being raised without its mother or adult cat will take slightly longer to litter train; so, keep this in mind when you begin the task of litter training your kitten. - Place the kitten in the box 1/2 hour after play or meals.
But they do take some special care. Weaning. Mothers usually begin to wean their kittens at about 4 weeks of age. By 8 weeks of age, the kittens are eating solid food. Older kittens who are still with their mothers may occasionally nurse, but this is more for comfort and reassurance than for nutrition. In general, kittens should not be removed from their mothers until they are at least 8 weeks of age. Kittens seperated from their mothers at too young an age require special care.