Paramedics at the scene were then targeted in “a second unexpected attack” by the RSF, the group added in a statement late on Friday, ITV reported.
The death toll is expected to rise as communication blackouts in the area hinder efforts to verify casualties.
The strike marks the latest escalation in the two-year conflict between the RSF and the Sudanese military, whose fighting has increasingly centered on the oil-producing Kordofan states.
“Killing children in their school is a horrific violation of children’s rights,” UNICEF Representative for Sudan Sheldon Yett said in a statement on Friday.
“Children should never pay the price of conflict.”
He said UNICEF urges all parties “to stop these attacks immediately and allow safe, unhindered access for humanitarian assistance to reach those in desperate need.”
In a related development, hundreds of civilians have been killed across the Kordofan states in recent weeks as intensified clashes shifted from Darfur after the RSF seized the besieged city of el-Fasher.
Sudanese military airstrikes on Sunday killed at least 48 people, most of them civilians, in Kauda in South Kordofan.
Meanwhile, UN Human Rights Chief Volker Türk warned that Kordofan could face atrocities similar to those documented in el-Fasher.
RSF’s capture of el-Fasher was accompanied by executions of civilians, rapes, sexual assaults, and other abuses.
Thousands of residents fled, while thousands more are feared dead or trapped inside the city.
Separately, the RSF and the Sudanese military have been battling for control of the country since 2023.
More than 40,000 people have been killed and 12 million displaced, according to the World Health Organization, though aid agencies say the true toll is likely far higher.