You have a bucket. You draw out a few red balls, and state that the "theory" is that the bucket contains only red balls. You emphasize that this is a falsifiable theory because it can be completely disproved by drawing out any other color of ball. For dramatic effect, you can proceed to draw out a blue ball.

If you have the opportunity to make it slightly more complicated, you can have another bucket, and state that your hypothesis about this bucket is that it contains 50% red and 50% blue balls. You start drawing out balls, and keep track of the count on a screen or whiteboard. The more balls you draw out, the more obvious it is that the ratio is something more like 90% red, 10% blue. This gives you the opportunity to talk about instances where the theory can't be disproven instantly by a single observation, but the burden of evidence nonetheless accumulates against it over time.