Yes,
jumping jacks are harmful.
But also, what causes you to attempt to find out if
jumping jacks are harmful, is also harmful. With just a "yes or no" answer about jumping jacks, it leaves the poster (and the reading public) to seek other ways - like, okay, how about castor oil? How about eating baking soda?
Babies are very, very inconvenient little folks, and you have to start out your motherhood surrendering to the inconvenience, and surrender to self-sacrifice.