What do you call the act of moving sideways by jumping and extending your legs in a V before jumping? By that I mean extending your legs in a V and then putting your legs together while jumping so as to form an I and on and on? Is there a particular name for this? I am thinking there might be one since kids do that a lot.
You're thinking of jumping jacks—but you forgot to mention that your arms are also lifted outward in combination with your legs:
: a conditioning exercise performed from a standing position by jumping to a position with legs spread and arms raised and then to the original position
// We did a few jumping jacks to warm up.
Also, you don't normally move from your original position.