Processed kitten food has a slightly higher protein and fat content than the adult varieties, but nothing much else different apart from that.

You get a better source of protein from raw meat, chicken and various other foods that a cat/kitten can be fed on such as scrambled egg yolks or some grated cheese sprinkled over a main meal, even a little bit of peanut butter (no added sugar) licked off the finger on the odd occasion as a treat - cats love it.