Brussels (AFP) - The mass retreat of the Islamic State group from its territories in Syria and Iraq has left Europe grappling with the risk of foreign fighters returning home.

But in Belgium, authorities are also turning their attention to repatriating children stranded in the war zones.

With an estimated 500 citizens who have reached or attempted to reach the conflict zones, Belgium has the highest number of jihadists per capita in the EU.

The government has said there are at least 100 Belgian children under 12 years currently in Syria, who were either born there or were taken to the country with an adult.

In May, a Belgian jihadist took his three-year-old daughter to Syria without the knowledge of her mother, despite being under electronic surveillance.

Justice Minister Koen Geens said the children are usually brought home via Turkey under the protection of Belgian police officers.

He revealed that Belgium and NATO partner Turkey had set up a gathering point on Turkish territory for those children wanting to come back, usually but not necessarily with their mothers.

"Fourteen children have returned," said Interior Minister Jan Jambon, "11 of them under six years old."

- 'Small' threat from children -

The flow of foreign fighters to the conflict zone has partly reversed since the IS group's self-declared caliphate in Iraq and Syria began crumbling in the last year under assault from regional, US-backed and other foreign-backed forces.

An EU report in December said a third of the estimated 5,000 European jihadists who went to Syria and Iraq had returned to Europe, and some may have orders to carry out attacks.

An unspecified number of wives and children have also returned to their homes throughout Europe, with officials concerned that they too could be planning violence.

Jambon told lawmakers last month that the chances are "relatively small" that children so young have been radicalised.

But he said these children would probably need psychiatric and other follow-up care to recover from traumas they might have suffered during the conflict.

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Such support must constantly be "refined" to ensure the children settle properly into Belgian life, prosecutors from Belgium, France, Spain and Morocco said at a meeting this week in Dutch-speaking Flanders.

Until now, children's aid officials in French-speaking Wallonia told AFP that they have cared for only four children in a specialised educational centre.

Under Belgian law, a judge must review cases of children who are at least 12 and have committed an offence in war zones, but this has not yet happened in the region.

That is a signal to some observers that the Belgian government has not done enough to try to help bring back its citizens from the Middle East battlegrounds.

- 'Complex problem' -

"It's a complex problem. What can we do? Dispatch teams to identify the children? If the parent is dead, his nationality may be difficult to ascertain," a senior security official said on condition of anonymity.

"In Turkey, Belgium provides consular services to help with repatriation, which is not the case in Syria and Iraq," the official said.

"But the minor will have first had to cross the border."

Bahar Kimyongur, a Belgian researcher who works with UN human rights experts, said Turkish President Recep Tayyip Erdogan holds a key to the solution, at least for children stranded in the northwestern Syrian province of Idlib.

"Erdogan has support through the Turkmen brigades. The Turks have lots of contacts and room for manoeuvre," Kimyongur told AFP.

The Turkish army is due to deploy in Idlib with Russian and Iranian forces to restore security to the province in line with the Astana accords.

Through his family and other contacts on both sides of the Turkish-Syrian border, Kimyongur helped two mothers, a French and a Belgian, bring back their young children.

The last case grabbed the Belgian media spotlight and prompted an emotional outpouring as the country waits for the return of another child.