Western Australia's corruption watchdog has questioned the WA Police Force's decision not to charge an officer with assault over his treatment of a 13-year-old child in state care.

Key points: Officers were told a child was "smashing up" a Child Protection office

Officers were told a child was "smashing up" a Child Protection office One officer repeatedly pushed the boy in the chest, then the boy struck him

One officer repeatedly pushed the boy in the chest, then the boy struck him The CCC found the officer should have been charged with assault

The Corruption and Crime Commission (CCC) on Monday released a report into the incident, which occurred in February 2018 after officers were called to a regional Department of Child Protection and Family Support (DCPFS) office following reports the child was "smashing up the reception area".

WA Police said the incident occurred in South Hedland.

CCTV footage shows an officer directing the child to sit down, before what the CCC described as "repeatedly pushing the child in the chest and gesturing in a threatening manner in front of the child's face".

The 13-year-old attempted to walk away, but was stopped before he swung out his right arm and struck the officer's shoulder.

The boy was handcuffed and taken to a nearby police station, where CCTV footage showed him spitting in an officer's face.

He was charged with criminal damage for his actions at the DCPFS office and two counts of assaulting a public officer.

He pleaded guilty to criminal damage but not guilty to the assault charges.

Magistrate found force was 'harmful'

During the trial, the magistrate acquitted the child of assault charges while heavily criticising the actions of police officers, and raised concerns that the arrest of the child was unlawful and force used by the officer against the child was harmful.

The report said the magistrate questioned the honesty of two of the officers' evidence and expressed concerns that both the officers present, and the reviewing inspector, had failed to recognise the force used against the child was unreasonable.

The honesty of two of the officers' evidence was questioned by the magistrate. (File picture) ( ABC News )

The WA Police Force later investigated the incident and found there was no record of the child being provided an opportunity to participate in an interview, and the child was not provided his rights.

It also found two of the officers negligently made misleading and inaccurate statements and one "failed to conduct a proper and adequate investigation".

The investigator found the officer's actions did not amount to criminal conduct, but because the child was not told he was under arrest, the actions were unprofessional, unnecessary and appeared "oppressive and bullying".

Two of the officers involved were fined, while one was ordered to undertake further training.

Officers should have faced criminal charges: CCC

The CCC said in its opinion the investigation had failed and criminal proceedings for assault should have been instituted against the officer in question.

"The Commission remains of the view that criminal proceedings should have been instituted and the matter resolved in court," the report said.

"The finding that there was insufficient evidence to prefer a criminal charge against the officer for assault was supported by flawed reasoning that was inconsistent with conclusions reached in the subsequent disciplinary action.

"In the Commission's opinion, the WA Police Force used contradictory reasoning to justify not criminally charging the officer with assault, on the one hand, and sanctioning the officer for use of unnecessary force on the other hand".

WA Police deny need for charge to be laid

The WA Police Force said it had reviewed the CCC's findings and acknowledged that the watchdog had a different view on whether the officer should have been charged.

But a spokesman said the Force maintained "the grounds for a criminal prosecution were not met".

Internal disciplinary measures were taken against the officers involved and penalties were imposed that the spokesman said were comparable to those which may have been imposed by a criminal court.

It was also noted that in its report, the CCC had commented that despite the difference of opinion on whether to lay charges, "the WA Police Force had otherwise dealt with the matter appropriately and reached conclusions that were open" to it.