Love this video about the famous "marshmallow test". Watch this with your kids and talk to them about the challenges of waiting for something worth waiting for. Connect this with the reality that people waited hundreds of years for Jesus. If you have older kids or no kids at all check out the wikipedia page for some history on this famous experiment on deferred gratification.
Also on these boards
The Marshmallow Study Revisited - experimental design
Whenever the owners of this house with a pool came home, they found puddles of water near their pool. They believed the neighbours kids waited until they went out, to use the pool....so they installed a camera and this is what they saw....