Figures obtained by the NSPCC show that 126 cases of under-18s committing child sexual abuse were reported to Lincolnshire Police over the last three years.
The statistics were obtained from the force under the Freedom of Information Act (FOI) as part of a nation-wide fact finding mission.
Across England and Wales, more than 5,000 child sex offences committed by under-18s were reported to the police.
But the NSPCC says the true figure could be much higher, as not every force was able to provide relevant data when responding to the FOI request.
From the 34 police forces that did supply information, a total of 5,028 offences were recorded where the perpetrator was under 18, with some as young as five or six.
The alleged crimes included rape and other serious sexual assaults which were reported between 2009/10 and 2011/12.
Nearly all of the offenders, 98 per cent, were boys. And where the relationship was recorded, at least three out of five victims knew the abuser.
More than a third of the offences were said to have been committed by a family friend or acquaintance and one in five by family members.
The findings come in the wake of a report by probation inspectors last month which found police, social workers and teachers were missing the warning signs that a child may sexually offend.
“We hope our findings will ring alarm bells with the authorities that this is a problem which needs urgent attention,” said Claire Lilley, policy advisor at the NSPCC. She said the charity was treating more and more children who had carried out online grooming, harassment in chatrooms and ‘sexting’.
She added: “Evidence shows most young people who receive behaviour changing treatment early on, such as that offered by the NSPCC, will not continue to sexually abuse others or grow into adult offenders.”
Call the NSPCC on 0808 800 5000 if you are worried about a child. Children and young people can call ChildLine on 0800 1111.