You can't just sit your teen down for a talk and expect it all to instantly sink in. The trick is to find creative, experiential strategies that can help instill them with the financial savvy and optimism that'll serve them well as adults.
We play a game at restaurants where we never turn over the bill until all three of us independently guess the total. Trent loves it because he tries to win every time. That's just another thing we do to show him what things really cost.
You have to talk to your kids about money from a very early age, as this is when good habits start to form. Make sure that your kids come into contact with money, learn where it comes from and understand how it is used.