Image: Woman with mobile phone and credit card, smiling © Pando Hall, Photographer

Theoretically, giving your teenager a credit card can be a smart move. You can help build his or her credit scores and supervise how the card gets used while your kid is still under your roof.

But like so many other aspects of parenting, the theoretical doesn't always work in the real world. The more I observe teenagers, the more I understand why many parents would no more give their adolescents a credit card than they would hand over a loaded gun.

(My husband says what he remembers hearing most often from his parents during his teenage years was an exasperated, "What were you thinking?" The inevitable response: "I dunno.")

The problem with kids, said money expert and mom of three Janet Bodnar, is that they think like kids.

"Kids just don't get that (the card) is not money, that it's a loan," said Bodnar, the editor of Kiplinger's Personal Finance magazine and author of the book "Raising Money Smart Kids." "They will charge right up to their credit limit."

Bodnar, who didn't get credit cards for her three now-grown children, has a wealth of anecdotes about parents who did -- including the financial-services executive who was sure he'd sent his daughter off to college with a sound knowledge of how credit cards should be used."

Liz Weston

Liz Weston

She called from college and said, 'I'm charged up to my credit limit. Do I get a new (card) for next month?'" Bodnar said, laughing. "You think they know, but they don't know."

A big problem with providing credit cards to kids is that it takes a lot of time to do it right: to explain the rules, go over the bills every month and enforce consequences when the kid screws up.

"That's a lot of responsibility for parents," Bodnar said, and yet another chore that has to be fit into busy lives.

And Bodnar isn't convinced all that effort will pay off.

"As long as your name is on that card, they will not take full responsibility for it," she said. "Most kids don't learn to manage their credit cards until they have to pay the cards on their own."

Then again, telling your kids to just say no to credit cards is shortsighted. Most college students have them, and using credit cards responsibly (paying on time and in full) is one of the best ways to build the sound credit scores your kids will need to rent apartments and get mortgages someday.

Bodnar suggests you tell your kids to wait until they've had several years' experience managing a checking account on their own (first with an ATM card that can be used only to withdraw cash, then with a debit card that can be used for purchases) before they apply for their first credit card. She said her children got their first cards when they were seniors in college.

"All three of my kids have good credit ratings," said Bodnar, whose children are college graduates in their 20s. "They became good credit consumers."

It's somewhat harder for college students to get a credit card since the Credit CARD Act went into effect last year. Now they're supposed to have their own income or get an adult co-signer.

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But if they get turned down for a regular card, they may be able to get a secured credit card, which offers a low credit limit in exchange for a deposit of cash (typically $200 to $1,000).

Liz Weston is the Web's most-read personal-finance writer. She is the author of several books, most recently "The 10 Commandments of Money: Survive and Thrive in the New Economy" (find it on Bing). Weston's award-winning columns appear every Monday and Thursday, exclusively on MSN Money. Join the conversation and send in your financial questions on Liz Weston's Facebook fan page.