A third of children in the UK use blogs and social network websites but two thirds of parents do not even know what they are, a survey suggests.
The children's charity NCH said there was "an alarming gap" in technological knowledge between generations.
Even when parents had put controls on what youngsters could access, almost half the 1,003 children aged 11 to 16 surveyed said they could disable them.
The NCH said families had to learn more about technology to protect children.
A tenth of the 11-year-olds who took part in the survey said their parents did not know about the people with whom they communicated online.
And 13% revealed they were never supervised while using computers at home.
John Carr, the NCH's new technology adviser, said: "Children are pretty clued up when it comes to technology but they often lack the worldly wisdom to steer them away from its potential hazards.
"That's where parents come in. But our research shows they need to increase their knowledge if they want to protect their children."
The survey also found that 69% of parents thought they knew less than their children about mobile phones.
The NCH and the supermarket chain Tesco are launching a parents' technology guide, called IT? Got IT! Good!, which is being distributed at stores.
The chief executive of Tesco Telecoms, Andy Dewhurst, said: "Young people are often in the driving seat when it comes to new technology, and mobile phones and internet use can be of huge benefit for families.
"For example, parents can use texting to stay in regular touch with their children.
"However, all new technologies bring some risks and we believe that if parents talk to their kids and stay in touch with technology then they can be much more aware of how young people are using their mobiles and computers and can understand and help prevent those potential risks."
Meanwhile, a Mori survey of 2,300 11 to 16-year-olds in England and Wales has found that three fifths liked the idea of using computer games in the classroom. Half of those aged 15 and 16 did not.
It was commissioned as part of Teaching with Games, a project led by the Bristol-based research body Futurelab.