The only type of milk that is suitable for managing the specific nutritional demands of kittens is milk from lactating cats, period. Cow's milk is inappropriate for newborn kittens. Cow's milk can cause tummy upset and diarrhea and contains too much lactose and not enough protein, fat and energy. Formula that is made for human babies also is not suitable, as it too has insufficient amounts of fat and protein. A mother cat's milk and kitten formula are the only ways to go. Be safe, smart and do the right thing for the fluffy cuties.