When Karyn Hodgens' son was 7, money went through his hands like sand through a sieve. As soon as he got a couple of dollars from his allowance or a birthday gift, it was spent.

Frustrated, his parents sat him down one night at the computer and showed him – on an Excel spreadsheet – how a single $100 investment could pile up faster than a stack of Lego bricks.

Using 10 percent monthly interest as a starting point, the graph on the computer screen zoomed upward, piling up $985 in two years and hitting $30,450 in five years.

"His eyes went 'ping.' You could see the light bulb going on. That graph was such a visual," recalls Hodgens.

The money lesson was simple: If you save it, it will grow.

More than five years later, that "light bulb" moment became Kidnexions, a Rocklin-based company whose mission is to turn children into savvy savers and investors. Founded by Hodgens, a former fourth-grade teacher who loves math, and her husband, John, a software engineer, its sole product so far is "KidsSave," an online learning tool for kids ages 6 and up aimed at putting some fun into saving and investing money. It also takes some burden off parents.

"Kids are capable, as long as you set up the environment to enable them to manage their money," says Hodgens, whose two sons are now teenagers.

In the current economy, where even adults are struggling to master money-juggling skills, the need to get kids schooled in personal finances takes on a whole new resonance. According to a 2007 study by Visa, only 5 percent of adults surveyed learned money-management skills while in elementary or high school; 41 percent said they were self-taught or learned those lessons "the hard way."

"The earlier children become financially literate, the better off they will be as adults. … Young people need to understand from a young age that money is hard to come by and often isn't a question of what you want but what you need," said state Superintendent of Public Instruction Jack O'Connell.

Equipping kids early with that knowledge is a passion for Hodgens, who teaches summer math camps and money-management classes for kids in Roseville, Folsom and Carmichael.

In an after-school classroom at Del Dayo elementary school in Carmichael recently, she walked seven boys and five girls through a lesson. While the topic – "the power of compound interest" – would cause many adults' eyes to glaze over, these fifth- and sixth-graders were tuned in.

They started with two pieces of string, measured and cut to specific lengths, every inch representing $10,000. One string, the white one, represented what happens when an 18-year-old saves $100 a month, earning 6 percent interest, until reaching retirement age at 65. The second string, a green one, represented the total if the same money was "stuck in a mattress" until age 65.

She had them cut two more strings to represent the same investments, but for someone who started seven years later, at age 25.

The students busily cut their four pieces of string, then taped them to a ruler. Hanging together, the long, dangling strings vividly illustrated her point. The green strings – the proverbial mattress money – were considerably shorter.

Holding up a ruler, Hodgens focused on her message: The white string for the 18-year-old saver was about six times longer, indicating the benefit of interest compounded over time. "Look, it's not just longer, it's hugely longer," she enthusiastically told the class.

"Is 'hugely' a word?" asked a sandy-haired boy in blue jeans. "Probably not," quipped Hodgens, "but I'm a math teacher."

In dollar terms, the 18-year-old in her example had accumulated more than $313,000 by age 65. The non-investor, whose money had sat in the proverbial mattress, had maxed out at a measly $56,400.

Like the computer graphic that wowed her 7-year-old, "It's real important for kids to see the visual," Hodgens said afterward.

Some of Hodgens' money-management lessons already appeared to be paying off.

Have a personal finance question? Contact the Bee's Claudia Buck at (916) 321-1968 or The Sacramento Bee; P.O. Box 15779; Sacramento, CA 95852.