The NSPCC is calling for social media sites to do more to make their online platforms safer for the millions of children who use them by bypassing the age restrictions. Claire Lilley, NSPCC's head of child safety, said the risks to 11 and 12-year-olds need to be evaluated by the companies.
There is a significant jump in the numbers of children who have a social networking profile at age 11 - which coincides with the move to secondary school for most UK children
We estimate that around half of the UK's 11 and 12-year-olds have a profile on a social networking site with a minimum age of 13.
Age verification is a nut that social networking sites are yet to crack.
We want social networking sites like Facebook and Twitter to take a pragmatic approach - if younger children are determined to use social networking sites for over 13 year-olds, the sites can't simply turn a blind eye.
"This research underlines the urgent need for social networking sites to take their young users' safety much more seriously.
"We believe in the right of children to go online without fear of being bullied or harassed, and this cannot be achieved until social networks put adequate resources behind safeguarding and user verification policies."
The NSPCC are calling for social media sites to acknowledge that many of their users are under the age of 18, in order to do more to safeguard their child users.
The comments come as new research by the children's charity found that around half of the UK's 11 and 12-year-old regularly use social media, and of these, a quarter said they had been upset by something on it.
A quarter of children aged between 11 and 12 who use social media have been upset by something on it over the past year, new research from the NSPCC has revealed.
A poll of more than 1,000 youngsters also found that a fifth of children who had been upset by an online incident such as trolling, bullying or being sent inappropriate sexual messages, experienced this every day or almost every day.
Justice Minister Damian Green admitted more work was needed to help children be supported through the court process. Responding to the NSPCC report that highlighted failures in adequate care of young and vulnerable witnesses at criminal proceedings, he said:
There are a range of measures available to help reduce the anxiety of attending court, including giving evidence behind a screen or the use of a registered intermediary, which has increased significantly over recent years. We are also trialling pre-recorded evidence for young and vulnerable witnesses.
We recognise that more work needs to be done.
I have ordered an investigation into how we might reduce the distress caused to victims from cross examination from multiple defence barristers without compromising the fundamental right to a fair trial.
Currently just two per cent of child witnesses in criminal court cases receive guidance on criminal proceedings from registered advisers, the NSPCC findings reported, and yet at least half said they were unable to understand some of the questions they had been asked.
The research showed that more than 50 per cent of child witnesses reported symptoms of stress ahead of a trial, including panic attacks, self-harm and difficulty sleeping.
Children giving evidence in court in sexual abuse cases need to be given more support, with many suffering from stress ahead of a trial, the NSPCC has said.
The children's charity warned some cases are collapsing because not enough is done to help vulnerable witnesses, it has been reported.
Fewer than a quarter of the 23,000 child sex offences recorded in England and Wales last year resulted in prosecution, according to the NSPCC.
Chief executive Peter Wanless told the BBC news website: "These children have to publicly relive the most traumatic, upsetting and humiliating experience of their lives in order to try and get justice."
The number of calls made to a charity helpline reporting sex abuse this summer has been "significantly higher" than last year, the head of NSPCC helpline said today.
John Cameron said that the Jimmy Savile scandal is "changing the way in which people react to abuse".
"There appears to be a clear shift and the public now seem better equipped and more confident to report their concerns.
"The Savile scandal has shocked the nation but has also increased public awareness of how difficult it is for children to speak out and how crucial it is for adults to report any suspicions or concerns they have straight away."