Orphaned siblings, thought to be from the UK, have been removed from a detention camp in northern Syria.
Amira, Heba, and Hamza, were taken to Raqqa along with 24 other orphans, the United Nations children's agency said.
The BBC spoke to 10-year-old Amira last week, when she described how her mother and father were killed during bombing.
The siblings, whose parents are believed to have left London for Syria after joining the IS group five years ago, are now with Save the Children.
Their mother, father, two sisters and two brothers were killed in April during the last battle in Baghouz before IS surrendered.
Amira, Heba, eight, and Hamza, six, were being held in the Ain Issa camp, which contained around 200 IS supporters but is now empty, following the advance of Turkish troops.
Amira also said she had a grandmother in the UK but couldn't remember her name, and that she wanted to go home.
The UK government said it was continuing to look for relatives of the three children.
BBC Middle East correspondent Quentin Sommerville, who met the children in the Kurdish-controlled camp, said: "They had a really last-minute escape just before the Ain Issa detention camp fell... Turkish troops were advancing - the UN got in there and scooped up the kids."
The children are now in Raqqa, which will soon be under regime control, he added.
"Damascus has in the past allowed the children of extremists to be repatriated to their countries, but only countries they have diplomatic relations with," our correspondent said
"Britain doesn't have any embassy or any consular assistance inside Syria. So it's going to be very complicated to get the kids out of there."
On Sunday, Kurdish officials said hundreds of IS-affiliated foreigners escaped from the camp amid a Turkish offensive.
The Turkish military has launched a major cross-border operation in north-eastern Syria against a Kurdish-led militia alliance.
In a statement, Save the Children said the three children were unharmed. The charity added: "Yesterday over 900 people including 700 children fled the annex in Ein Issa [Ain Issa], where foreign families were staying. Most of them are unaccounted for. We are deeply concerned for their wellbeing and safety of the children among them.
"Children in Syria who have fled ISIS-held areas are innocent. They are swept up in horrific events far beyond their control and deserve to be safe and protected."