But expert argues children of terrorist can be reformed with care.

Five Sydney children trying to return from Syria have every chance of being reintegrated into Australian society, an expert says.

The three sons and two daughters of Australian Isis recruit Khaled Sharrouf were taken to the war zone by their mother, Tara Nettleton, soon after Sharrouf's departure in December 2013.

Nettleton's family are now reportedly trying to repatriate her and the children, one of whom was photographed holding a severed head at age 7. US Secretary of State John Kerry described the image as "one of the most disturbing, stomach-turning, grotesque photographs ever displayed".

One of the teenage girls has reportedly been married to Australian Isis fighter Mohamed Elomar.

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Nettelton flew with return tickets via Malaysia to hide from Sydney Airport officials their intended destination.

Prime Minister Tony Abbott says Nettleton will face the full force of the law if she returns to Australia.

But Immigration Minister Peter Dutton said yesterday that children of terrorists would be treated as a special case. The children could become wards of the state if their mother was imprisoned.

There is no evidence that Sharoouf, who slipped out of Australia in late 2013 using his brother's passport because his own had been cancelled, wants to return to Australia. Police have confirmed he faces an arrest warrant in Australia on terrorism offences.

ANU radicalisation expert Dr Clarke Jones said the children had clearly witnessed "atrocious acts" and suffered bouts of indoctrination and desensitisation.

"They have certainly been well indoctrinated in the Isis beliefs," Dr Jones said.

Separation from their parents could deepen their trauma but there was a good chance they could be reintegrated with guidance and proper schooling.

"I do think it's possible at that age to help them and steer them in the right direction with positive role models and positive counselling," he said.

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"They're going to need all the love, attention and care from more stable people than what their parents are."

Dr Jones said he feared for their safety if they were identified by members of the Australian public and said they could need protective custody.

He had previously been abused for encouraging compassion toward Muslims, he said.

"If they [abusers] don't like what I say then God, I'd hate to think how they'll treat kids with such a notorious father," he said.

Some comments on social media are wishing death on the entire family - one user hopes they will be beheaded for trying to leave Isis.

Asked about the family, Mr Abbott said if the children had committed a crime, they would be treated by the Australian courts the same way as other juvenile offenders.

"But the point I want to stress is that criminals will be punished whether they're young, whether they're old, whether they're male, whether they're female, whether they're criminals abroad or criminals at home," Mr Abbott said.

"Criminals will be punished and to participate in the kind of barbarism that we have seen so often in the Middle East is just wrong. It's morally wrong and it's a crime under Australian law and it will be punished."

Nettelton's father, Peter Nettelton, said yesterday he had not seen his daughter in more than a decade and had met only two of his grandchildren. He did know the family's whereabouts and would not comment on the report.

"I still love my daughter and hope she comes home safely," he said outside his Sydney home.

Australia used controversial new counterterrorism laws in December to make even visiting Isis' stronghold of al-Raqqa province in Syria a criminal offence punishable by 10 years in prison.

Australia has cancelled the passports of scores of suspected terrorists, preventing would-be jihadis from leaving the country and stranding foreign fighters overseas.

Australia also plans to pass a law soon to give the Government the power to strip citizenship from dual nationals who are suspected terrorists, even if they are not convicted of a crime.

Sharrouf was among nine Muslim men accused in 2007 of stockpiling bomb-making materials and plotting terrorist attacks in Sydney and Melbourne.

He pleaded guilty to terrorism offences in 2009 and served less than four years in prison.

Shia militias take charge of Ramadi operation

Iraq's Shia militias launched an offensive intended to put a stranglehold on Isis (Islamic State) fighters in Ramadi, taking the lead from Iraqi security forces who lost the western city to the extremists just over a week ago.

The operation to cut supply lines and besiege the city from the northeast is "led and managed and planned" by Iraq's popular mobilisation units, a loose formation of Shia militia groups and volunteers, according to Ahmed al-Assadi, a spokesman for the units. There was "co-ordination and co-operation" with other military forces, he said.

Iraqi Prime Minister Haider al-Abadi had initially held back from sending the Shia militias to the western province of Anbar, amid sensitivities over dispatching them to a majority Sunni area.

Local Sunni tribes, fearing both Isis' advance and potential militia abuses, had been split on whether the Shia paramilitaries should join the battle. However, they were ordered to the province last week after the fall of Ramadi highlighted weaknesses in Iraq's regular security forces and the local council requested the militias' assistance.

US officials have indicated that they do not object to the mobilisation units' involvement as long as they work under the command and control of the Iraqi Government. On a front line in Anbar, army soldiers said they had no doubt the militias were needed to retake the province.

"Of course we can't fight without the popular mobilisation," said Captain Hussein Najib, an officer with the Iraqi Army's 11th Division who was manning an artillery unit in Garma, west of the capital. "The mobilisations are Iraq's unity; they are our right hand."

Their religious fervour was needed in the face of Isis' extremism, added one of his men.

The operation aimed to secure the remaining areas in neighbouring Salahuddin province before moving on to Ramadi, Assadi said.

He said militia forces had received new supplies of "modern weapons" 'that would be used in the battle and "surprise the enemy".

- AAP, AP, Washington Post-Bloomberg