Panos Moumtzis, the UN Refugee Agency regional coordinator for Syrian refugees, said plans were in place to help 4 million people in Syria - 2 million who had been displaced and 2 million who need help in their homes - and up to 1.1 million refugees.
"We're really talking about helping a quarter of the Syrian population. One in four Syrians is in need of humanitarian assistance and I'm afraid this number is deteriorating," Moumtzis told the International Peace Institute in New York.
The United Nations hopes to raise $1.5 billion to fund Syria aid assistance at a donors conference in Kuwait on Jan. 30. Moumtzis said 55 organizations, including 12 UN agencies were currently responding to the crisis.
Turkey, Lebanon, Jordan, Iraq and Egypt have been flooded with tens of thousands of refugees. Moumtzis said 30 percent of these refugees were housed in camps and the rest were living outside camps in villages and towns.
"Refugees pour across the borders day and night," he said. "More than half of them are children. This is a children's refugee crisis. It's heartbreaking when we see these children arriving and particularly what we see in the days that follow."
"Many of them are withdrawn, we hear from the parents about bedwetting. These children have experienced and witnessed some of the most horrific scenes, seeing their parents or loved ones killed, their homes destroyed, their schools effected," he said.
Moumtzis spoke of one woman crossing the border into one of Syria's neighbors in the middle of the night carrying one son under each arm and then waiting for her elder son to arrive.
"She waited and she waited and the son never made it. His body was brought later on by some people who came behind her," Moumtzis said, without elaborating on how the boy had died.
The United Nations says more than 60,000 people have been killed during a 22-month-old revolt against Syrian President Bashar Assad, which began with peaceful protests but turned violent after Assad's forces tried to crush the demonstrations.
More than 100 people were shot, stabbed or possibly burned to death by government forces in the Syrian city of Homs, a monitoring group said on Thursday, and fierce fighting raged across the country.
Moumtzis said there were a lot of young refugees because it was common for families to have 8 to 10 children.
"Most of the kids come with an adult ... most of the times it's at least one of the parents," he said. "It's extremely difficult for these kids to articulate what they have seen."
NEW YORK (Reuters) -- More than half the 642,000 refugees who have sought refuge from the Syrian conflict in neighboring countries are children and the number of people fleeing could almost double by June, said a senior UN official on Thursday.