The gap is widening between what kids do online and what their parents think they do.

A new study shows that children are online twice as much as their parents think they are and nearly one-quarter are getting away with forbidden online activities, according to security company Symantec, which commissioned Harris Interactive to do the poll.

Parents also may be disconcerted to learn that the survey showed that 23% of children have had an encounter with a stranger on the Internet and 7% reported having met someone in the real world from the Internet.

"Kids today have never known a world without the Internet and interacting with their peers via social networks is common practice," said Pete Findley, CEO of Giant Campus, a technology consulting company, in a written statement. "Unfortunately, without parents who are knowledgeable about the Internet and actively involved with what their children are doing online, kids could learn of the dangers of the Web through a damaging experience."

According to the poll, which was conducted this past June, parents of children under 18 think their child is online an average of three hours a week, but those children admit to spending an average of seven hours online a week. And 23% report doing online activities that their parents would not condone.

The survey also showed that 21% of kids say they've experienced "inappropriate" material online that made them feel uncomfortable. Eighteen percent have had an experience with cyber bullying or cyber pranks, and 20% said they wished their parents were more interested in using the Internet.

"We know children, and particularly teens, are engaging in online activities their parents would be shocked to learn about," said Marian Merritt, Internet safety advocate for Symantec, in a written statement.

In May, research from anti-spyware software firm Webroot also showed that what parents think their kids are doing online and what they're actually doing are two different things. More than 70% of the surveyed children, ages 11 to 17, said their parents ask them about their online activities, but they may not be getting accurate answers.

According to Webroot, more than half of the teens surveyed said they buy things online, but 71% of parents said their children never buy anything over the Internet. Forty percent of the kids polled said they use instant messaging and social networking Web sites, like MySpace and Facebook everyday, while only 30% of the parents said their children participate in these sites. And 45% of the kids say they spend an average of three or more hours on the Internet a day but 76% of parents polled said their children spend an average of two hours or less on the Internet.