My kitten loved nutro natural care. It is not going to do your kitten any harm that you gave it cat food, but your should switch it to a kitten formula immediatly. Kittens require more fat, protein, vitamins and minerals that are in "kitten formulas" rather than in cat foods.
Also, it is important to feed your kitten a premium brand like Nutro, Science Diet or Iams. Not only do they have much higher quality ingredients, each bag is the exact replication of a specific recipe. With grocery brands (non-premium brands), each bag is made up of different things to fill the nutrition requirements. That is not a good thing.
Feeding your kitten a premium brand also reduces the amount that they eat because they are filling their nutrient levels much faster than eating a "cheaper" food. This also reduces the amount of stool your kitten produces and makes healthier, harder and darker stools that are easier to clean up. Less stomach gas too.
If you are confused about what brands are premium, visit your local PetSmart or Petco. "Authority" cat food at PetsMart is also a good economically premium brand own by PetsMart. A good general, beginning list of premium foods include Nutro, Science diet, Eukanuba, Authority and Nature's Recipe. See what your kitten likes and thrives on.
Again, I can't stress enough how important a kitten formula is for your little one. It gives him/her every advantage of developing into it's full potential by providing the right amount of nutrition for every cell in his/her body.
Good luck and let us know how your kitten is doing! Would love to see some pics!
Take care, hoped this helped...and sorry so long!!