Money you put away in savings earns interest that is added to the principal. Then you earn interest on that, causing savings to build faster.
Compound interest, though, works against you when you borrow. Interest accrues on the debt over time, and you can end up owing much more than you borrowed.
Savings accounts also remain a valuable teaching tool, despite today's dismal interest rates. Children with bank accounts can learn to become disciplined savers by watching their balance grow with each deposit. Indeed, some of today's top financial minds learned money basics through a childhood account.
Brian Rogers, chairman of the Baltimore-based investment firm T. Rowe Price, said years ago that he developed the savings habit from a passbook savings account that his parents opened for him when he was 6. The bank for years paid a rate of 5 percent, so compound interest was easy for the young Rogers to see.
Rogers, 56, held onto the account for decades -- partly for sentimental reasons -- but closed it this year when the bank was acquired.
Financial experts suggest parents explain to kids that these are highly unusual times of very low rates. And banks and credit unions that visit schools to teach about finances point out that some interest is better than none at all.
"We tell students the secret to getting rich slowly ... is the miracle of compound interest," said Lisa Monthley, chief deposit officer with New Windsor State Bank in Carroll County.
Students usually have piggy banks, Monthley said, and the amount in there today will be the same many months from now if left alone.
"If you put it in the bank, it will earn interest and compound over time," she said. "And if you leave it alone and add to it, you will slowly get rich."
Still, Monthley sympathizes with Simon.
"We all feel the same way," she said. But at least, she added, he is earning some interest and his money is secure in the bank.
Here are a few tips for parents wanting to teach the value of compound interest:
Shop around: You're not going to find a financial institution paying a generous interest rate, but you can find places that offer more than 0.04 percent.
Credit unions, for instance, tend to offer higher rates on deposits than banks. You can also find more generous rates at institutions farther away if you're willing to bank online.
Sallie Mae Bank, for instance, offers savings accounts with an annual percentage yield of 1 percent that's compounded daily. On a $500 deposit, the balance would grow by $5.03 the first year. Not much, but better than the 20 cents that Simon will earn.
Check Bankrate.com to find out the highest rates on savings accounts being offered in your city or nationwide.
Or consider putting money in a certificate of deposit, in which the rates are higher. The drawback is that money will be tied up during the term of the CD and you will forfeit part of the earnings if you withdraw the cash early.
Parents as bankers: The experience of seeing a savings account grow with interest has a powerful impact on children, said Lew Mandell, a financial economist with an expertise in children's financial literacy. But if banks won't provide that experience, parents can do so themselves, he said.
Mandell suggest that parents pay the interest, depositing the money quarterly in the child's savings account. It doesn't have to cost much, he said. At 3 percent annual rate, parents would pay out a little more than $15 the first year on a $500 initial deposit.
"To make it more interesting, think of giving the child 5 percent a year," he said. At that rate, parents would pay about $25.50 the first year. After 10 years, the child's account would grow to $821.81.
When higher interest rates return, Mandell said, parents can stop playing banker.