Moving Target

Why is it when people are in large groups the small children among them pick one or two of the older folks to madly run circles around, literally? It seems to be an activity of which they never tire, too. Also, why is it that this particular activity can send almost any parent through the roof in mere seconds? I have seen parents who look to be using every ounce of will not to punt their children across the room, and have felt the urge myself...