A Scout leader has been charged with the alleged indecent assault of a teenage girl at a national event in Sydney's south west.

Police said the 14-year-old girl reported the incident, which happened on Monday afternoon at the Australian Scouts Jamboree being held at Cataract Scout Park, near Appin.

Campbelltown police said they were not called until Friday afternoon when they attended the site and commenced an investigation.

The 63-year-old West-Australian man was arrested by police just after midnight on Saturday and charged with aggravated indecent assault of a child under 16 and was granted bail.

He appeared in court yesterday, was granted bail and is due to appear Campbelltown Local Court on Wednesday.

A statement from Scouts Australia said the organisation acknowledged there was a delay in the incident being reported to NSW Police.

"This was due to a lack of understanding of Scout protocol and procedures by some leaders," the statement said.

"Once the incident came to the attention of the Scout authorities' onsite at Jamboree the NSW Police were notified immediately.

"Scouts education and training for leaders on child protection will continue nationally."

Scouts said the man had a valid working with children's check and that the organisation had now revoked the man's membership.

Scouts Australia Chief Commissioner Chris Bates said the Scouts had zero tolerance for any type of abuse.

"Scouts is recognised as having the highest standards of child protection procedures in place," Mr Bates said.

"We are constantly reviewing processes in place to protect young people in our care and to deal swiftly and decisively with any complaints.

"Scouts has provided immediate support to the child and to their parents, and will continue to do so as they require."