Determining the age of kittens can be done by looking at their behavior, their eyes and their weigh. The age of kittens is very important, both for socializing the kittens and also to know how to care. First week kitten is smaller than your hand, eyes beginning to open, ears still flat. After 5 weeks eyes have changed from blue to another color and kittens have begun to pounce and leap. If the kitten does not start nursing right away, or if he seems to have trouble getting the milk. Never feed a kitten cow’s milk or human baby formula as this causes stomach problems.