I would teach them that every item, even grocery store items, has more than one price. You can pay a lot for it, or you can pay a little. What you pay is where your choice comes in. For example, if you have even $20 of savings, you can buy a dozen items when they're on sale instead of one item not on sale. This has some far reaching consequences:
1. You pay less per item than the guy down the street
2. You therefore have greater buying power than the guy down the street.
3. The more money you can save, the greater your buying power is.
4. The greater your buying power, the less money you spend, which leads to more savings and even greater buying power.
5. The longer you can keep your savings, so long as they're in an appropriate place, the even greater they become. This is the gift of compounding interest.
6. THIS, kiddies, is how the rich stay rich.
This comes with provisos, though, the biggest being that buying things you don't need is not a saving. This might be a time to mention Mike Tyson, his pet tiger and his low net worth.