Hurry! Don't let that balloon touch the floor.
3 or 4 balloons
Arrange the players in a circle on the floor and have them number off. Put the highest number in the center to act as 'it'. He/she should hold a balloon and suddenly drop it as they call out a number. The holder of that number then should try to catch the balloon before it touches the floor. If he succeeds, 'it' tries another number. If it touches the floor then he is "it'.
You can play elimination style where those who don't catch the balloon are out and play continues until only two players are left. Then an "umpire" can drop the balloon for the last two to determine the winner.