A police officer strip-searching a child at a Sydney under-age music festival this year told the boy to "hold your dick, lift your balls up and show me your gooch" in one of at least 25 potentially illegal searches on the day.

In another incident a police officer touched a teenage boy's testicles and ran his hands over his buttocks, while, in yet another, the support person provided to a 13-year-old girl being strip-searched was herself a 17-year-old girl from the Red Frog charity.

Three specific examples of boys aged between 15 to 17 being told to touch their genitalia at the Lost City music festival at Sydney Olympic Park on February 23 are being scrutinised in a NSW Police watchdog inquiry.

None of the boys was found to have any illegal drugs on them and each has denied having been in contact with drugs.