Wales watchdog's concern over child sex abusers' help
The children's commissioner for Wales says a lack of services to treat children who show signs of sexually harmful behaviour is a serious problem
Keith Towler said children in some areas are at a greater risk of sexual abuse from their peers because there is no consistent approach.
Latest figures show 243 reports of child abuse in Wales by under 18s.
The Welsh Government said it has recognised a need for a nationwide approach to tackle the issue.
Children who have committed a sexual offence, or show signs of doing so are sometimes highlighted to social services by a family member or teacher.
They are assessed and, if necessary, referred for specialist help.
But Mr Towler said that provision is not available everywhere.
"There is still a postcode lottery in place. That is a big, big problem," he added.
"Generally, we could be at risk of failing children.
"Unless you are prepared to travel and unless someone is prepared to take a referral from an outlying area, you're not going to get the resources you need."
He called on councils and health authorities to look at how they are making resources available for children who display sexually harmful behaviour.
The Welsh Local Government Association (WLGA) said local authorities regard the safeguarding of children as of paramount importance.
It said it is working with the Welsh Government and local authorities to deliver three regional hubs to provide specialist services.
The Welsh Government said it is developing an all-Wales protocol on the management of young people who engage in sexually harmful behaviour.
About a third of all cases of sexual abuse against children are found to be carried out by other children or young people.
That figure is based on a range of statistics and studies from bodies like the Ministry of Justice, the police and children's charities.
The most recent figures obtained under the Freedom of Information Act show that between 2009 and 2010 the four Welsh police forces recorded 243 reports of child sex abuse, where the suspect was under 18.
However, experts warn that most of these crimes go unreported, so actual figures are likely to be higher.
Sexual assault referral centres across Wales help victims of abuse and see agencies like the police and social services working together to offer help.
Young sex abusers might also receive help from charities like Barnardo's Cymru.
The charity's Denise Moultrie said most youngsters they work with are in their mid teens, although some are aged eight to 11. Most are boys but about 8% are girls and young women.
"But in terms of our there children below that age, who are engaging in sexually inappropriate behaviour, then yes, you will see children of four, five and six," she said.
"Clearly, it's very important to try and work on that early. The younger children are, the more they can learn to do things differently."
Both Barnardo's Cymru and the NSPCC Cymru agree that, across Wales, it is not always a case that those that need help receive it.
Des Manion, national head of service for NSPCC Cymru, said: "As a service centre here in south Wales we'll get contacts from a number of local authority areas, which suggests to me that provision isn't uniform.
"What's really important is the issue around assessment and treatment for young people with harmful sexual behaviour, so they can be helped to manage or reduce their harmful behaviour.
"But it is a bit of a postcode lottery in deciding where you get that service from or whether it actually exists.
He said a uniform level of service, consistency delivered, was needed so that all children get the same quality and standard of service