Wedding Favours -- with small balloons, this could be a fun favour and even elegant depending on what string is used.
wind string around balloons of various sizes, apply fabric stiffener, let it dry and pop the balloons. You can hang them from the ceiling or place them on a table along with bold flowers to create a beautiful centerpiece.
Absolutely genius - blow up balloons, string them together w/a needle and thread, and hang.
Tie a string to a balloon and to each child's ankle and then have them try and pop each others. Could have more on hand to keep the game going for those whose balloons popped early.