As we know cats are considered kittens till around twelve months of age. From starting the month of 1-4 weeks, the kittens are fed by the bottle with milk, five weeks and the older ones can be offered canned food, but still, need to be continued bottle-fed until they are matured enough.
During this period of growth and development, the kitten needs complete and balanced kitten food.
Kitten food is quite different than adult food, they have different nutritional needs than adult cats, so they need kitten food to support those needs.
At two months old a kitten should be eating kitten food as it generally contains more calories than adult food to support growth. Something like Royal Canin Kitten Food or Whiskas Kitten Food. They are a great source of protein and calcium for the growth and development of kittens.
Adult cat food contains 26-40% protein in the diet whereas kitten requires 30-45% protein.
Kittens need plenty of calories to grow and play, but they do have small stomachs, so they need food that delivers a large number of calories in small portions.
Adult food contains less protein and calcium as they are quite mature and result in weight gain.
If all of a sudden two months kitten starts eating cat food, your kitty gets sick, has diarrhea, and even vomiting. Thus kittens shouldn't eat adult cat food until they are fully matured.
Therefore cats under one year should be eating kitten food unless your vet tells you to switch to adult cat food.