The suspected rape of a girl by a six-year-old boy was one of 28 sexual offences involving children aged under 10 recorded in the last four years by North Wales Police.
Figures show that 160 crimes involving under-10s were recorded by the force since 2011.
However, anyone under the age of 10 cannot be legally held responsible for a crime.
But the offence or allegation of a crime is still recorded by police.
The figures, released after a Freedom of Information request, show that a six-year-old boy is believed to have raped a girl under 13 in 1997. The offence was registered in 2013.
It was among four rapes recorded by the force in the last four years – the three other rapes involved suspects who were all aged nine.
One of those took place in 1971, although it was recorded this year.