By Nancy Shute

Parents of teenagers know how important texting and social media sites like Facebook are to the over-13 set. But if we think we know what our kids say and do on the sites, we're kidding ourselves. My 13- and 14-year-old nephews kindly remind me more often than I'd like of my cluelessness, and a new survey confirms that I'm not the only parent who has no idea.

Common Sense Media, a nonprofit that tracks children's use of media, commissioned a poll of teenagers and their parents this spring. It turns out that teens are way more active online that most parents realize:

* 49 percent of parents said their child was 13 or older before starting to use the Internet unsupervised. Just 14 percent of teenagers said they were that old.

* 23 percent of parents said their children log onto social networking sites like Facebook more than once a day. But 51 percent of teenagers said they check in more than once a day.

* Just 4 percent of parents think their children check social networking sites more than 10 times a day; 22 percent of teenagers said they're online that often or more.

* When it comes to "sexting," or posting explicit photos, 2 percent of parents believe their child had posted naked or near-naked photos or videos of themselves or others. But 13 percent of teens admitted they had done that.

As one of those parents who needs to wake up and smell the latte, I'd better ask my nephews for more in-depth instruction. Sexting is just one worry. The survey, which polled 1,013 kids in the seventh to 12th grades and 1,002 parents, also found that 39 percent of the teenagers had posted something they later regretted and that 28 percent shared personal information online they normally wouldn't have shared publicly. Nothing posted on the Internet is ever truly private, and it's there forever, so it's not hard to imagine college applications being derailed by derogatory comments about teachers (which 54 percent of teens say they had posted) or hacking someone else's social networking account (as 24 percent of the teens said they had done).

Ah, but kids need to wise up, too. Only 14 percent think their parents know their Facebook password; in fact, 51 percent of parents said they do. And 82 percent of parents check their child's online profile regularly, while barely one quarter of children think they're being watched. Tip to observing parents: Monitoring children's social networking activities is essential to helping them become safe and wise users of the Web, but hacking into their accounts or using monitoring software isn't the way to do it, according to an article by my colleague Lindsay Lyon on Mastering Social Media Dangers. Instead, explain how even privately posted photos or information can become permanently public, and don't be afraid to set rules on how your children use social networks. One clever idea: Ask the kid to help you build your own Facebook profile.

Social networking is here to stay. I'm greatly enjoying becoming part of communities I've found on Twitter and am even getting used to Facebook, though I use it more for professional networking than for keeping up with friends. And I'm facing up to having to add teaching my little girl to have a healthy life online to my long list of parental responsibilities.