Boy, 10, reported for sexual activity involving girl. 5
A 10-year-old boy has been reported for sexual activity involving a five-year-old girl, it has emerged.
The boy was the youngest in Wales reported for sexual offences against another child during two years.
The NSPCC said with offences involving very young children "we have to question the environment in which they are growing up".
There were 158 sex offences by children against children recorded over two years in three of Wales' police forces.
The youngest alleged offender was a 10-year-old boy in the Dyfed-Powys area who was reported for sexual activity involving a five-year-old girl. He received a caution.
Some of the most common crimes were boys offending against girls they knew.
The NSPCC said most victims of this sort of crime are girls who knew their alleged abuser, and that up to two-thirds of sexual abuse on children was committed by other young people.
The charity put in a Freedom of Information request which revealed 8,000 under 18s across Wales and England were accused of sexual offences.
South Wales Police recorded 70 cases over two years - 31 of these led to convictions, while there were 61 reports to North Wales Police, with 50 people charged.
A further 27 cases were reported to Dyfed-Powys Police, with 25 people charged.
Across the three forces, nine 11-year-olds were investigated between 2012/2013 and 2013/2014.
Gwent Police could not provide full statistics although the force said there had been 78 child-on-child sex offences reported in one year.
Des Mannion, NSPCC Wales' head of service, said: "It's deeply concerning that thousands of children are committing sexual offences, including serious assaults and rape.
"For very young children, such as those of primary school age or younger, we have to question the environment in which they are growing up that has led to them behaving in this way."
He said although shocking, the behaviour can be turned around if caught early and the warning signs are recognised.
"It could be that they have seen sexual activity that they are just too young to understand and are copying what they've seen," said Mr Mannion.
The charity says parents can help keep their children safe by teaching them the 'Underwear Rule', which explains that the area covered by underwear should not be touched by anyone else.
- The NSPCC said any adult worried about a child or in need of help and advice can contact its helpline on 0808 800 5000. Children and young people can contact ChildLine on 0800 1111.