Young people are being "raised online", spending their free time on internet sites such as Facebook and Myspace, according to research.

In its Behind the Screen: The Hidden Life of Youth report, the Institute for Public Policy Research (IPPR) found that children between the ages of 13 and 17 are spending more than 20 hours a week online.

They were also found to be staying up late at night, communicating on social networking sites and leaving their mobile phones on all night so they didn’t miss any text messages.

The report said that four out of five children aged five to 15 have access to the internet at home. More than two-thirds of 12- to 15-year-olds also said they mostly used the internet unsupervised at home, with older children admitting to hiding their online activity from parents and teachers.

When asked about her parents' views on her internet use, one 16-year-old said: “My mum will ask sometimes ‘Is it safe?’ but she doesn’t really know.”

As a result the IPPR is calling on the Government and internet companies to do more to protect children from inappropriate content. It said that while many websites have their own guidelines, these are not always properly enforced.

The researchers found that searching the Youtube website for the term 'happy slap' delivered 117 videos posted in the last week, while 'street fight' found 312 videos.

Kay Withers, the report's author, said: "The internet offers great benefits and opportunities for young people. But with kids spending an ever-increasing amount of time online, parents need to be reassured about what they are looking at.

"The Government needs to improve media literacy programmes for kids and to make sure parents are aware of how they can support young people's positive online experiences.

"But more importantly, internet companies need to take more responsibility for the content on their sites and promote acceptable behaviour."

The full report and recommendations are to be published in April.