A sharp jump in calls to a helpline about online sexual abuse has sparked an appeal for parents to discuss internet safety with children receiving smartphones, games consoles and tablet computers this Christmas.
The NSPCC said there were 3,716 Childline counselling sessions about the issue in 2015/16 - a 24% increase on the 2,994 the previous year.
Over the past three years, the number of contacts to Childline about online sexual abuse has surged by 250%.
The category can include grooming, child sexual exploitation, sexting, being made to perform sex acts on webcam, meeting in person, and viewing distressing sexually explicit content.
Some children contacted Childline because they felt trapped by their situation, because they felt guilty and ashamed, were being blackmailed, or were considering meeting in person.
A 14-year-old girl told the service: "I met this guy through social media and he was really nice. He told me I was beautiful and I felt that I could talk to him about everything.
"He asked me for some topless photos which I didn't think was a big deal, so I sent him a few. But now he's turned really nasty and is threatening to post them online if I don't send him more.
"I'm really worried and embarrassed and I don't know what to do."
The NSPCC said it is vital that parents talk to their children about being safe online with tablets, smartphones and games consoles.
Peter Wanless, chief executive of the charity, said: "The web can be a fantastic place for children and young people to socialise, explore their interests, and learn, but every parent buying an internet device should be aware that there are risks too and think about installing parental controls.
"In the last year we've seen a staggering rise in online sexual abuse, with many children turning to Childline when the situation has escalated.
"Often groomers will use devious tactics to lure in young people and manipulate them into situations that leave them feeling frightened and ashamed.
"The NSPCC has lots of resources to help parents talk about online issues so that they can help keep a child safe and happy online."
Advice for parents includes exploring sites and apps together with their children, asking about things they might see online which make them feel uncomfortable, and reassuring them that they will not overreact.
Minister for digital and culture policy Matt Hancock said: "It is essential to make sure children can enjoy all the benefits of the internet as safely as possible - whether that is for playing games, gathering information or staying in touch with family and friends.
"As well as teaching children to be aware of online safety in the curriculum, keeping children safe online is a joint effort, and there are a range of simple and practical steps parents can take this Christmas to better protect their children from online risks.
"This includes using the NSPCC's online resources and the UK Council for Child Internet Safety guide for parents."