ISIS thugs are forcing children to play soccer with decapitated heads to make them more brutal killers, a new study claims.

The report — backed by Canadian Romeo Deallair’s Child Solders initiative — and issued this week by the British counter-extremism think-tank Quilliam Foundation details horrific evidence of how the terror group radicalizes its young.

In the study, called Children of Islamic State, the authors state that young children are repeatedly exposed to violence to desensitize them for roles as fighters.

That includes having them participate in beheadings — as has been seen in videos proudly issued by the bloodthirsty militants — and encouraging the “children to participate in public brutality, including holding up decapitated heads or playing football with them.”

The 100-page report details accounts of how ISIS’ brainwashing campaign of children, starting at a very young age, leads to the breakdown of their psychological well-being.

“Self-esteem is usually destroyed, and they become convinced that war is the sole option. Thus, as they become adults, they do not consider peacekeeping alternatives and tend to formulate violent solutions to problems.”

It compares ISIS' tactics to those of the Nazis in pre-war Germany.

“Elements from Nazi Germany can be glimpsed in the systematic indoctrination of children through schools and training camps in IS,” the reports says.

It also suggests that young girls — who are often repeatedly raped — have a higher risk of their lives being ruined by ISIS' psychological terror.