If you are looking for a quick and easy activity for an event, this site shows you how to make some quick and easy kites with A4 paper and some barbecue kebab skewers. Kids of all ages seem to like kites so don't restrict yourself to the youngsters! Be careful though not to fly near overhead power lines or near busy roads. Also where it says string you really need something like linen thread. Ordinary string would be too heavy.
For an idea of what is possible with kites look at this site (or google for images of Kites )