Risk-taking is for the young—except, it seems, when it comes to investing.

The 2008 market panic, last year's "flash crash" and the latest burst of volatility are proving to be more than many young investors can stomach. As a group, people in their 20s and early 30s are less comfortable taking risk than they were before the financial crisis, according to recent surveys—leading them to hunker down with safe assets at a time when many financial planners say they should be rebalancing into risky ones.

"We had Depression babies," says Bill Finnegan, a senior managing director with MFS Investment Management, a Boston-based asset manager. "Now I think we have recession babies."

Investors who eschew risk at such a young age might be setting themselves up for disappointment. Without the compounding effects that come with investing in equities for a long time, stock-less investors might find it nearly impossible to accumulate a big enough nest egg to retire at all, let alone in their 60s.

"It's hard to build a lot of wealth without taking at least some risks in the markets," says Colorado Springs, Colo., financial planner Allan Roth.