You will need:
A parachute (play or otherwise)
Several small balls (foam or tennis balls work well).
Players hold the canopy taut at chest height with 2 or 3 small or foam balls on the surface. 3 or 4 children underneath the canopy have to try to knock the balls off whilst those around the canopy try to keep them on. The players underneath win if they knock all off in an agreed time.