Christian aid agency World Vision is calling for urgent international action after a new deadly strain of mpox was declared a global health emergency.
The virus has killed hundreds in Central and West Africa, and the World Health Organization fears that it will cross into other continents. The first case outside Africa was reported in Sweden on Thursday.
World Vision said that children in poorer nations are particularly at risk.
In the Democratic Republic of Congo, over a third of the 7,851 reported cases (39%) are children. Some 240 children have died from the virus in the DRC, amounting to 62% of the total death toll from mpox in the country.
World Vision said that children in DRC face a "grave" risk of dying and there was a "pressing need" for "swift intervention", including the distribution of vaccines, clean water, sanitation and hygiene facilities to prevent more deaths.
National Director of World Vision DR Congo, Aline Napon said, "Children are particularly vulnerable to mpox, especially in low and middle-income countries, including those suffering humanitarian crises and where health and social services are weak or non-existent.
"Children are especially at risk where they are living in refugee camps, overcrowded urban settlements, and where malnutrition, a lack of clean water and sanitation, and poor health services exist."
She is calling for a rapid response from the international community to support the roll-out of vaccinations and public education programmes, and step up treatment for those already infected.
"World Vision's experience in tackling Ebola and COVID in humanitarian situations tells us that there is no time to waste," she said.
"People in DR Congo and other impacted countries need immediate free treatment for mpox. There must also be an immediate immunisation programme set up to prevent further infection and mortality. We cannot stand by while children die from this deadly but preventable disease."
