A 12-YEAR-OLD girl has told police she was sexually assaulted, possibly by up to five teenage boys, in bushland at a western Sydney park.

A joint strike force has been established to investigate the allegations.

The girl was alone when she went to meet friends at Progress Park in Auburn on September 9.

She has told police she was sexually assaulted in isolated bushland ­adjacent to the park, not far from a dimly lit footpath and playground.

At the time, an Eid festival — marking the holy Islamic holiday — was in full swing in Progress Park.

Hundreds of people, including families and young children, flocked to the event that afternoon.

The alleged victim emerged from the bushland and reported the ordeal to a family member.

The Sunday Telegraph understands detectives are investigating whether up to five boys, with ages ranging from early to mid teens, were involved in unlawful group sex with the girl.

The 12-year-old was taken to hospital for a sexual assault examination. The investigation is being led by the Child Abuse Response Team and the Sex Crimes Squad. A police spokeswoman confirmed the investigation was under way.

Police have potential suspects under investigation, some of whom are related to well-known crime families in southwest Sydney.

Child-on-child assaults traverse sensitive and complex legal territory.

While the age of criminal responsibility in NSW is 10 years old, there is a legal presumption that a child can’t commit a crime because they don’t know the difference between right and wrong.

Last week charges against two 12-year-old boys accused of sexually assaulting a six-year-old were dropped.

A magistrate, referring to a precedent, withdrew the charges ruling, in part, they were too young to understand what they did was wrong.