Almost 30,000 reports of children sexually assaulting other youngsters, including 2,625 alleged attacks on school premises, have been made to police in the last four years, figures reveal.
The data released by 38 of the 43 police forces across England and Wales, in response to freedom of information requests, shows reports of so-called "peer on peer" abuse rose from 4,603 in 2013 to 7,866 last year - an increase of 71%.
But almost three-quarters of cases (74%) reported to 36 forces between April 1 2013 and May 31 2017 resulted in no further action, according to the figures obtained by the BBC's Panorama.
The investigation found 2,625 reported sexual offences, including 225 alleged rapes, carried out by under-18s on other children happened on school premises, including primary school playgrounds, across 31 force areas.
Figures from 30 forces show reports of sexual offences by children aged 10 and under have more than doubled from 204 in 2013-14 to 456 in 2016-17.
Some children - anonymised to protect their identities - who were interviewed by the current affairs programme told how they felt bullied, let down and isolated after reporting abuse.
"It's not what actually happens that has the worst effect on you, it's what comes after it. It's the being disbelieved - it's the people failing you," said one.
Another said: "We'd be on the bus, they'd throw things at me or shout things and make comments. It's not always even him, it's his friends."
Abused children and their parents also spoke of struggling to get help from schools or the authorities.
One victim said: "There was no talk about the police or telling his parents or taking it further, it was only really 'oh block him', or 'stay away from him in lesson'."
Another child's parents said: "I couldn't actually believe that we're in the 21st century in Great Britain and we are allowing sexual abuse to continue... and for victims to go unsupported."
Government guidance tells teachers they have a legal duty to report allegations of sexual assaults on children by adults.
But Panorama claims there is no such duty when a child is accused of sexual assault, with schools advised to follow their own child protection procedures.
However, the Department for Education told the programme: "Sexual assault is a crime and any allegation should be reported to the police."
An investigation by the Press Association earlier this year revealed that children as young as five had been excluded from school for sexual misconduct.
The data released by local authorities showed hundreds of school pupils had been permanently or temporarily kicked out of the classroom in the past four years after being involved in sexual acts, including watching pornography and sharing indecent images.