No problem. It is well known that kicking your feet is exercise. Of course, if you throw your feet hard, regardless of your own life and death, this will not happen under normal circumstances.

Maybe your parents are worried about this, or maybe they think that falling your foot will affect your personal image, and they are afraid that others will say that your child didn't teach well. I believe you are a good boy, so please feel your parents' concern for you.

I won't let your feet shake. I can find another way to exercise. You know what you like.