International charity Save the Children has warned 200,000 Syrian refugee children are at serious risk from freezing temperatures.
The BBC reports many families have fled across the borders to Turkey, Jordan and Lebanon, as winter sets in the Middle East.
More than two million are displaced inside Syria, as fighting between government forces and rebels continues.
Save the Children says many are living without proper shelter and clothing and may not survive the harsh conditions.
The charity is launching an appeal for funds, saying the more vulnerable - the very young, the elderly and the sick - are most at risk if help does not reach them in time.
Some of the Syrian families who have crossed borders into neighbouring countries have been registered and settled in camps where their basic needs are looked after, the BBC's correspondent in Beirut says.
But he says many others are living in makeshift conditions without adequate shelter, bedding or warm clothes to face the torrential rains and sub-zero temperatures that are normal in many parts of the Middle East in winter.