Let nature take its course. My experience is they stop when they are ready. The mother will not tolerate it indefinitely, and the kitten will be forced to move on.
Nothing. It is best for kittens to nurse until they are 10 to 12 weeks old, they build up their immune system from antibody's from their Mother's milk.
If the kitten is already eating solid food in addition to nursing, then there is no problem. Often kittens will continue to nurse after weaning because it is comforting.
