It is their nature. So you as an individual will ripen from whatever potential you have but also be more influenced a lot by the parents. You can't say that karma is a closed thing. Like my karmic energy right now is interacting with all of yours. If you all attack me then I feel negative.
Different things change.
Same thing with you and the work environment that you have, your home environment and things. Those interactions are always changing you. And so you are always a changeable being. So as a baby growing older, you are continuously under the influence of your parents. You have your potentiality in a few areas, and then you have your parents interplay with you.