“I say no, no, no,” he tweeted. “Their parents are no longer fellow citizens.”

When ISIS controlled parts of Iraq and Syria, an estimated 41,000 people from other parts of the world left their homes to join the group — about one-third of them from Europe, including the Caucasus. Some took children with them and others had children there. Thousands were killed and thousands more managed to slip away, many of them making their way home and risking prosecution as terrorists.

But as ISIS lost the last of its territory early this year, tens of thousands of survivors crowded into refugee camps that were built for far fewer people. At least 29 children died just in traveling to Al Hol or soon after arriving at the camp, the World Health Organization reported in January.

Violence, disease and despair are common there, and food, medicine — and sometimes even clean water — are scarce. Gerrit Loots, a psychologist who led the Belgian team at Al Hol, said that women still faithful to the Islamic State threw stones at those who had renounced it.

About 3,000 women and 7,000 children from countries other than Iraq and Syria are held at Al Hol, according to the Kurds and the group Human Rights Watch. Many of them want to return to their home countries. The largest contingents are thought to be Russian and French, while Germany, the Netherlands and Belgium are also among the major nations of origin.

Some women who joined ISIS soured on it, but others believed fervently and even took part in atrocities. Children were indoctrinated and sometimes pressed into service. It can be difficult to determine who is guilty of crimes, who still adheres to radical ideology, and who might change with counseling.

A very few countries, including Kazakhstan and Kosovo, have repatriated many of their people from ISIS territory, including adults. Turkey, Russia and a few others have taken in significant numbers of children recently, mostly orphans, though more remain.