The conflict in Sudan has displaced more than one million children including 270,000 in the Darfur region, the United Nations Children's Fund (UNICEF) said, warning "many more are at grave risk."
Also, at least 330 children have been killed and more than 1,900 others wounded, UNICEF said in a statement on Thursday.
Fighting has raged in Sudan since mid-April between the Sudanese army and the paramilitary Rapid Support Forces.
Mandeep O'Brien, UNICEF representative in Sudan, said: "the future of Sudan is at stake, and we cannot accept the continued loss and suffering of its children."
"Children are trapped in an unrelenting nightmare, bearing the heaviest burden of a violent crisis they had no hand in creating – caught in the crossfire, injured, abused, displaced and subjected to disease and malnutrition," he added.
UNICEF said an estimated 13 million children were in "dire need" of humanitarian assistance.
The UN agency said it was ready to assist them but called for "safe, unrestricted access and guaranteed security to all areas where children are in desperate need".
It said the situation in the western region of Darfur, where 270,000 children are said to have been displaced by the fighting, was especially concerning.
UN relief chief Martin Griffiths also warned on Thursday that humanitarian situation across Sudan continues to deteriorate and the situation in Darfur is spiraling into humanitarian calamity.
(With input frrm agencies)