All the parties to the conflict, of which a large part is now integrated in the national army, are responsible for the forced recruitment of children into armed forces and groups.
Unicef also called for the immediate release of children associated with armed forces and groups, and their protection from reprisals.
The use of schools by armed forces and groups, even for a few days can have lasting repercussions.
They may be separated from their families, trafficked, recruited or used by armed forces and groups, economically exploited, or physically or sexually abused.
"Girls associated with armed forces and groups are often traumatised by years of abuse and sometimes have children of their own," the report said.
During the Sierra Leone war, an estimated 10,000 children were recruited or used by armed forces and groups, and at least 692,000 children suffered sexual abuse.
This tactic of war violates the sanctity of schools, turning them from safe havens into targets for bombing and recruiting grounds for armed forces and groups.
These include: clear directives by those in positions of authority within armed forces and groups to halt violations against children, meaning that children must not be recruited into the fighting, nor targeted.
In some areas, girls make up less than 2% of children released and passing through the demobilisation programme, despite making up around 40% of the children used by armed forces and groups.
Beyond this immediate destruction, in the majority of conflicts around the world, armed forces and groups are using schools for military purposes – occupying them as barracks or training grounds, or used for weapons stores or detention centres.
More than a thousand men and children have been pressed into armed service in Wau Shilluk and 12,000 children were used as soldiers by armed forces and groups across South Sudan last year, according to monitoring reports.
