You can start feeding your kitten dry food around 4 weeks, their teeth are already coming in. You start feeding the kittens real dry kitten food mixed with water or kitten formula. It is three parts dry food and one part water or formula. If you use formula you mix it according to the directions on the package. You need to feed them twice a day, morning and night. Make sure that you put it in a plate that the kittens can easily eat out of, remember they are small and cannot get down into a deep bowl, and make sure that there is enough room for all the kittens to eat around the plate or get more than one plate. You will need to do this anyway as they grow bigger.
Remember that they are still nursing and will do that as long as the Mother allows them to. They will not eat the food all at once and will periodically go back to the plate to eat more. It is OK if the mother is eating with them as it good for her to eat kitten food because of all the vitamins and minerals in kitten food. The Mother Cat should be eating kitten food before giving birth and through out the nursing process as this helps her get the essential vitamins and minerals that she needs for herself and her kittens.
Always keep their food bowls clean and always keep fresh water out for them. It is vital for them to be able to play, eat and sleep as they are growing so fast at this stage.
Everything is new and exciting to them, love them, care for them and remember to have them spayed and/or neutered when they are old enough. Your Veterinarian will be able to tell you the best time to spay and/or neuter your animals.