"Children as young as 10, 12 years old are being used in a variety of roles, as combatants, as messengers, spies, guards, manning checkpoints," Laurent Chapuis, the UNICEF regional child protection adviser for the Middle East and North Africa, said, PressTV reported.
"What is new is that IS seems to be quite transparent and vocal about their intention and their practice of recruiting children," he said.
Leila Zerrougui, the UN secretary-general's special representative for children and armed conflict, also said the IS militants are "abducting" children and "forcing" them to join IS. "They are brainwashing children and indoctrinating them to join their group".
"All the tools used to attract and recruit children are used by this group," she said, adding that children as young as 9 or 10 are used for "various roles."
Citing hundreds of interviews with people who fled or are living in IS-controlled areas, a UN panel of experts, known as the Independent International Commission of Inquiry on Syria, said that the Takfiri group "prioritizes children as a vehicle for ensuring long-term loyalty, adherence to their ideology and a cadre of devoted fighters that will see violence as a way of life."
The Takfiri militants have seized large swathes of land in Iraq and Syria. They have carried out horrific acts of violence in the two countries, including public decapitations.
In November, Human Rights Watch said that IS militants have tortured and abused children whom they detained near the northern Syrian city of Kobani earlier this year.
It said that that the children, aged 14 to 16, were among 153 Kurdish boys abducted by the IS militants on May 29 as they were returning home after taking school exams in the city of Aleppo.