The Dutch secret service warned on Wednesday of the danger posed by radicalised children returning from territory controlled by Islamic State (IS).
Rob Bertholee, chairman of AIVD, told a Dutch television broadcaster that many of these children could have received combat training.
"Boys can attend training camps from the age of nine," he said, adding that children of that age "or even younger" had likely been involved in attacks and executions. "Children in the IS area have lost their innocence due to all the violence," Bertholee added.
IS has released a series of propaganda videos and pictures showing young children engaged in weapons training, carrying out suicide bombings and executing prisoners.
In a report that AIVD released Wednesday, it warned that as IS loses more territory in Iraq and Syria and living conditions deteriorate more fighters could choose to return home, reported German press agency DPA.
It estimates that about 270 Dutch citizens currently live in IS controlled territory, with 80 estimated to be children, some of whom were born there.
So far only adults entering the country from Syria have been subjected to security screening, but this measure will be extended to children, who will be treated as "jihadi travellers" according to the report.
"Children as well as adults may have participated in the fighting or in other acts of violence," the AIVD report said. "It is possible that these experiences lower the threshold for the use of violence and can result in trauma."