The answer depends on the definition of the word "side." One, perhaps. I think this is a terrible question and is the kind of thing that will make children hate math. "Side" is a term that should really be reserved for polygons. In convexity theory, there is a notion called an extreme point that generalizes the notion of vertex (or corner) of a polygon. For this definition every point on a circle is an extreme point so it makes sense to say it has infinitely many corners. However, the notion of side is not as good. If the definition is line segment joining two vertices then the answer would be 0 for the circle. Both answers 1 and infinity are intuitively correct, I think.