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.
Kittens should be wormed around 6 to 8 weeks and kept flea free. Kittens should not go to new homes under the age of 8 weeks while 10 to 12 weeks is preferred as kittens learn their social behaviour during this time both from their mother and also from siblings. More Information: How to Care for Kittens which covers everything you need to know about raising and caring for kittens.