On April 30, the Syrian government, supported by Russian air power, began a large-scale offensive against rebels in the provinces of Hama and Idlib, forcing thousands of people to flee.
The Syrian forces have since regained territory from the rebels in the two provinces.
The UN has estimated that more than 400,000 people have been displaced since the onslaught started.
UNICEF said on Tuesday "children are bearing the brunt of intensifying violence in northwest Syria."
"More than 500 children were injured or killed in the first nine months of 2019, and at least 65 children have been killed or injured in the month of December alone," it said in a statement.
It said that recent intensified violence in areas of Maaret al-Noumaan, south of Idlib city, has pushed thousands of families to flee north.
"Since 11 December, more than 130,000 people, including over 60,000 children, have been displaced from southern Idlib, northern Hama and western Aleppo because of escalating fighting," the UNICEF statement said.
It added that the displacements are adding pressure on overcrowded camps near the Syrian-Turkish border and that many families still have no shelter and are sleeping in the open air despite the cold weather.
In Maaret al-Noumaan, the Syrian American Medical Association (SAMS) said it suspended its operations in two major hospitals as the situation deteriorated in recent days.
SAMS said these hospitals had been serving around 300,000 civilians before the escalation.
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