"Thirty-seven children were recruited [to reinforce rebel troops] in Rutshuru [north of Goma] two weeks ago," Jaya Murthy, spokesman for the UN Children's Fund (UNICEF), told IRIN.
Children separated from their families were more at risk, he said. The boys were forced to fight while the girls became "wives" to the soldiers.
"There has been an upsurge in the number of children being recruited since the latest violence began," Ishbel Matheson, spokeswoman for Save the Children, said. The NGO was taking care of several children who had escaped recently from the armed groups.
An estimated 3,000 children were being held by the armed groups before the recent violence broke out, she said, but numbers were expected to soar.
In the past year, the charity, which runs one of the largest programmes to reintegrate child soldiers into their communities in the DRC, had helped 2,200 children out of the armed groups and reunited most of them with their families.
Hundreds of schools were closed due to insecurity while children recruited numerous times had had their studies interrupted.
"UNICEF will build emergency classrooms and distribute school supplies when schools reopen," Murthy said.
"For these children it is a recurring nightmare," Matheson told IRIN. "Children who are forced into armed conflict suffer terrible physical and emotional damage. They are traumatised by being separated from their families and may witness executions, beatings and torture. Many young girls now have babies."
Attacks on schools by the armed groups were also common.
On 10 October, seven children and three teachers were abducted when they were ambushed outside their school in Masisi, northwest of Goma, capital of North Kivu. They were held for two days before they escaped. Two weeks later, an armed group attacked a secondary school in Shasha, 7km outside Sake near Lake Kivu. Twelve children escaped but one was killed.
"One child told me that they are scared to go back to school for fear of being attacked," Matheson said. "For these children, getting an education is their only hope for the future. If they can't go to school they lose that hope."
The NGO has been working with the affected children to reunite them with their families or place them in foster families. So far 250 unaccompanied children have been found since the latest fighting began.
Fighting resumed late August in North Kivu between forces from rebel group Congrès National pour la Défense du Peuple (CNDP), led by former general, Laurent Nkunda, and the regular Congolese army allied with patriotic militias.
Meanwhile, UNICEF is providing truckloads of clean water daily to Kibati and Mugunga, in addition to water purification posts and latrines to curb the risk of cholera spreading, Murthy said in a 11 November communiqué.
In the displacement areas, cases of measles continue to be reported. Previous measles vaccinations interrupted by the fighting would resume soon. "UNICEF will vaccinate up to 66,000 more children in the coming days/weeks," he said, adding that the spread could be exacerbated by the large population movement.
Three aid planes from the UK and USA left Goma on 11 November to distribute aid to thousands of displaced persons.
"Plastic sheets for shelter and blankets will help ward off respiratory infections," he said.
UNICEF is also planning to reinforce the dozens of feeding centres in North Kivu to curb malnutrition.