He believes there is no good age — or time — for a parent to open a credit card for their kids.
"When should kids get a credit card? Never," O'Leary tells CNBC Make It.
While some parents may make the case that getting a credit card could help their kids build credit and get a better credit score for the future if used responsibly, O'Leary has a better idea.
"[Kids] should get debit cards instead so they learn that you shouldn't spend on credit," he says.
"The fact is, the interest rates on credit cards are astronomical," O'Leary previously said. Paying so much interest "is crazy."
To teach his kids about money, O'Leary says he opened saving accounts for his children before they were 10 years old.
"I wanted them to see how money accrues interest," he says. "And it's a great thing to do because it helps them get into the concept of saving and investing and thinking long term."
According to a 2017 T. Rowe Price survey, 44% of parents are extremely reluctant to discuss money with their kids. But O'Leary says he thinks parents should start teaching the basics as soon as their kids hit kindergarten.
"I think kids should be taught at the age of five onward where money comes from," O'Leary told CNBC Make It last year. "We do a very poor job in North America telling kids about finance. We teach them sex education, geography, math, reading, all kinds of learning skills, but we don't tell them about debt. No wonder they get into trouble as soon as they get a credit card."
His advice is that families should have money talks as part of their daily dinner table conversations.
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