Nearly one-quarter of the world's children live in conflict or disaster zones, according to new figures from international children's charity UNICEF, released on Friday.
The UNICEF research found 535 million children live in countries stricken by war or natural catastrophes such as drought or flooding.
Children living in sub-Saharan Africa were most likely to be affected by war or disaster, followed by children in the Middle East and North Africa.
The figures have been released to mark the 70th anniversary of UNICEF's work supporting children in some of the world's most dangerous countries.
UNICEF executive director Anthony Lake said the number of children affected by war or disaster demonstrated the need for the organisation to continue to focus on their welfare.
"UNICEF was established to bring help and hope to children whose lives and futures are endangered by conflict and deprivation and this enormous figure - representing the individual lives of half a billion children - is a sharp reminder that our mission is becoming more urgent every day," he said.
The research analysed the impact of war, natural disasters and climate change on children, finding that 50 million children have been uprooted, with more than half of them driven from their homes by conflict.
Nearly half a million children live in besieged areas of Syria, almost completely cut off from humanitarian aid or basic services. In northern Nigeria one million children have been displaced and the ongoing civil war in Yemen affects 10 million children.
The research found a large proportion of primary school age children are unable to attend classes in countries including Afghanistan and South Sudan, where one in three schools have closed in conflict areas.
More than 90,000 children are still in need of basic support two months after Hurricane Matthew struck Haiti, killing almost 900 people.
The analysis revealed that there have also been some big strides in health, education and welfare for children over the past 35 years.
The number of children dying before their fifth birthday has halved since 1990, hundreds of millions of children no longer live in poverty and the rate of school non-attendance among primary school-aged children dropped by more than 40 per cent between 1990-2014.
In 2015 UNICEF responded to 310 humanitarian emergencies in 102 countries, the highest number in the history of the organisation which formed to support children after WWII.
UNICEF staff vaccinated 11.3 million children against measles in crisis-affected countries and provided education to four million children in emergency situation.
"Whether children live in a country in conflict or a country in peace, their development is critical not only to their individual futures but also to the future of their societies," Mr Lake said.
