Millennials, who came of age during the Great Recession, are skeptical of the stock market as an investment tool. Instead, many prefer to keep their money in savings accounts despite the current ultra-low interest rates.

And even at their young age, the people born between 1990 and 1999 are already concerned about retirement. According to a new report from TDAmeritrade released today, almost 45 percent are worried that Social Security or other government retirement programs won't be there when they retire, up from 39 percent who said this last year.

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Unfortunately, 47 percent believe a savings account is the best way to save for retirement, even though the average interest rate paid on a money market savings account is currently 0.47 percent, according to Bankrate.com. They're also doubtful about the stock market, with only 20 percent saying they think stocks are good long-term investments.

Nicole Sherrod, managing director of TD Ameritrade's Trader Group, says even though Millennials are worried about their long-term prospects, they see the near term with increasing optimism.

"We've seen a decrease in their overall concerns about jobs and unemployment," she said. "But they're increasingly concerned about the uncertainty of Social Security, government retirement programs and overall economic instability."

This group considers their parents, many of whom were hit hard by the financial meltdown, as the best resource for financial information. Sherrod sees that as a good thing, but she thinks parents alone aren't enough.

"Parents are doing a really great job," she said. "But only 10 percent report learning about finances from a teacher or at a course at school."

While Millennials understand the importance of higher education, they're also very concerned about its costs. Nearly 45 percent of respondents said they worry about having a large student loan balance when they graduate, with a third being anxious about repaying them and the same amount saying costs may prevent them from attending at all.

Although this group believes you should start saving for retirement by the time you're 27, they don't plan to do so until after they've bought a car, paid off their student loans, got married and bought a house. Sherrod says following this path could cost Millennials a lot.

"If they're not in the stock market, they're going to lose the benefits of compounding interest," she said. "Well, here we are with the stock market at all-time highs, and it's still not driving home to them that the stock market is the best way for them to save over the longer term."

Even before they finish college, Millennials are already acquiring credit card debt at an increasing rate. They now carry an average of $749 on their credit cards. That's up sharply from the $489 reported last year.