During a litter of kittens' tender earliest weeks, mama's milk is all that is necessary for health and survival. Soon after, however, weaning procedures begin -- when a queen cat slowly but surely starts her little ones on other foods. In general, weaning takes about four weeks in all.
The ASPCA indicates that mother cats usually start weaning the little fluff balls when they are about 1 month old. In general, kittens need their mother's milk until they are a minimum of 4 weeks old. The complete weaning process generally takes about a month, meaning that the wee kittens are usually fully weaned when they are between 8 and 10 weeks in age. Towards the end of the run, however, kittens should be receiving the vast majority of their dietary intake via food that is made specifically for kittens.
Once weaning begins, kittens are usually ready to start eating dry food part-time, even though they are still simultaneously nursing with mom. When it comes to getting kittens to eat "real" food, the process moves slowly.
The Humane Society of the United States indicates that weaning a kitten too early can sometimes bring upon unpleasant consequences -- particularly in the realms of chewing and suckling. If a kitten is taken off of her mother's milk too soon, she may continue suckling on random items well into adulthood, like blankets, wool sweaters or your most cherished winter coats -- no thank you.
Up until a kitten is roughly 1 month old, her dietary needs can be fulfilled completely through nursing. Because of this, it is absolutely unnecessary to offer kittens any other types of food whatsoever, whether dry or canned wet meals.
Absent Mother Cat
If for whatever reason a kitten's mother is absent from her life, then it is important either to search for a foster cat to temporarily "replace" mama for nursing purposes, or to purchase and use a "KMR" -- kitten milk replacer. KMRs are specifically designed to closely replicate the nutritional caloric offerings of a mother cat's milk with similar carbohydrates, fat and protein.