First, don't give them an allowance, instead, pay them a commission for doing things above and beyond those things that are expected of them. This will teach them the concept of "you work - you get paid" and "no work - no pay."
Second, teach them what to do with their money by making them save 10%, give 10% and live on 80%. They will learn the importance of helping others with your money, and having money in savings for emergencies.
Third, teach them to budget their money.
Fourth, as soon as they are mature enough, open a checking account for them and make them balance it every month. If they ever bounce a check, take them to the bank and have them personally apologize to the bank manager.
Fifth, don't buy them their first car. Instead, match any money they save dollar for dollar. You might want to put a cap on this, say $5000, you can buy a really nice used car for $10,000.
Finally, only buy things with cash, do not introduce them to using credit cards.