Buy some cheap ping pong balls from the dollar store.  You will need at least 2 per girl.  Draw faces on them if you wish.  Put them in a container.  Countdown 5-4-3-2-1!  Then throw them up as hard as you can!  The girls scramble to collect them and bring them back to you.  Limit the number each girl can collect so that every one can have a ball to find.