Kittens can safely stop nursing at around 4 weeks old. The weaning process involves slowly incorporating solid foods into the kitten's diet, and it is generally over by the time the kittens are between 8 and 10 weeks old.
Kittens should first be introduced to canned wet food made for kittens at 4 to 5 weeks old. Alternatively, they can be introduced to a milk replacement to teach them how to lap at liquids and runny foods before they are given a gruel to eat. At around 5 to 6 weeks old, hard food can be added to their diet, and by the time they are fully weaned, they can safely eat dry kitten food alone.