The NSPCC says lonely children, and those who rely on social media, are at risk of being targeted by predators while stuck inside during the lockdown.
Experts warn offenders will be looking to target lonely, socially isolated children as they increasingly spend time online.
More than 2,000 young people, aged between 11 and 17, were surveyed by the NSPCC last year, with four per cent confirming they had sent, received or been asked to send sexual messages to an adult online.
This more than doubled to nine per cent for respondents with characteristics that may make them vulnerable, including loneliness, greater usage of social media, unhappiness and liking attention.
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According to the NSPCC, the National Crime Agency is aware of online chats where offenders are discussing opportunities to abuse children during the crisis, while Europol has seen a surge in attempts by offenders to contact young people on social media.
Andy Burrows, NSPCC head of child safety online policy, said: “Through this survey, we have heard the voices of lonely, vulnerable children and discovered how much more exposed they are to online abuse.
“It’s particularly worrying during the lockdown as it is clear now that it has never been easier for abusers to exploit lonely children who are spending a lot of time online.
“This crisis has exposed the child protection cracks that were already there in social networks so now more than ever tech firms must step up and ensure their services are safe.”
The charity is calling on tech giants to improve steps to tackle child abuse by sharing intelligence of referrals and emerging and evolving risks with the authorities.
Experts also say parents have an important role to play in talking to their children about what they are accessing online.