A County Durham boy aged just five has become the youngest person in Britain to be investigated by police for "sexting".
The lad and his parents were spoken to by police after he took an intimate snap of himself and sent it to another child on an iPad.
The number of cases where children have taken explicit pictures of themselves and sent them to others has shot up in the past two years.
But police and children's charities are concerned that the age of those being drawn into the practice is getting lower and lower.
The five-year-old in County Durham was spoken to by officers from Durham Constabulary last year.
That made him the youngest person to be investigated for taking and sending sexually explicit selfies.
Detective Chief Inspector Steve Thubron of Durham Police said: "We record incidents in line with national crime recording standards, which we cannot deviate from.
"However, we deal with incidents proportionately and obviously do not criminalise children.
"Cases of 'sexting' are dealt with on a case-by-case basis with the focus always being on safeguarding and keeping children safe.
"We have worked with other agencies to provide advice and guidance to both schoolteachers and young people.
"We would urge any children who are worried to speak with a trusted adult or call 101."
More than 4,000 children have been dealt with by police for sexting since 2013. The most common age of these children is 13 or 14.
The shocking statistics have emerged from a Freedom of Information request to all UK police forces in an investigation by BBC Newcastle.
A 10-year-old boy - only just at the age of criminal responsibility - has also been cautioned by Northumbria Police for sexting.
The boy sent a sexual image of himself to an 11-year-old child using Oovoo - a free social media video and image sharing app.
Greater Manchester Police recorded the highest number of child sexters, with 695 cases looked into - including four seven-year-olds and four eight-year-olds.
It's illegal to possess, take or distribute images of someone who is under the age of 18 - even if the image is of yourself.
NSPCC campaigns manager Helen Westerman said: "For some children it is a voluntary action, something they want to do for a risk or a dare. But for others it is something they have been coerced into in some way.
"They may have been put under pressure by friends, peers or partners, but once it is out there it is out there. Once the picture has been sent they can't get it back, and the consequences of that can be devastating for the young people involved."
Last year a survey of teachers in the NASUWT union revealed more than half of teachers were aware of incidents of children sexting at their school, including primary-school pupils as young as seven.
A quarter of teachers who responded said they were aware of 11-year-olds sexting but the majority of incidents involved pupils aged 13 to 16. In one typical incident, a girl pretended to fancy a boy and persuaded him to take a picture of his genitals, which she then shared with others.
In another, a Year 9 pupil, aged 13 or 14, took explicit selfies of herself for a boy at another school, but classmates got hold of the photo and shared it, thereby distributing child sexual images.