Years ago a researcher conducted a now-famous and often duplicated experiment. He took a group of preschoolers, one at a time, and put them in a room with a marshmallow on a plate. He told each child, "You can eat this marshmallow now, or wait til I come back and I'll give you another one, and then you'll have two." He then left the room for 15 minutes, and we get to watch the child squirm, fidget, touch the marshmallow, smell it, pick it up, lick it, TRY so hard not to eat it. Some give in, some don't.
The really fascinating part is the follow up studies. What became of the children with self-control, and what became of those without? I heard a story about that today, and found a very similar report on youtube, which I hope you'll watch here. There are excellent lessons to be learned by us parents.
Then, just for fun, watch replications of the experiment, like this one.