Syrian children being massacred or left scarred for life
At least 652 children were killed last year in the war-torn country - a 20 percent increase from 2015 - and more than 250 of the victims were killed inside or near a school, the report said.
Cases of children being maimed or recruited into armed groups were also the "highest on record" last year, the children's agency found.
UNICEF said there was no let-up to attacks on schools, hospitals, playgrounds, parks and homes last year, as the Syrian regime, its opponents and the allies of both sides showed callous disregard for the laws of war.
The report found that at least 255 children were killed in or near schools in 2016.
"The depth of suffering is unprecedented. Millions of children in Syria come under attack on a daily basis, their lives turned upside down," said Geert Cappelaere, UNICEF's regional director.
"Each and every child is scarred for life with horrific consequences on their health, well-being, and future," he said.
UNICEF found at least 850 children were recruited to fight in the conflict, including as executioners or suicide bombers - more than double the 2015 number.
An additional 1.7 million youngsters are out of school and 2.3 million Syrian children are refugees elsewhere in the Middle East.
|Children were among the first victims of the regime's brutal crackdown [Anadolu]|
The figures come in a UNICEF report released two days before the sixth anniversary of the popular uprising that escalated into civil war.
The report also found that children were among the first victims of the regime's brutal crackdown.
On March 15, 2011, residents in the southern city of Daraa marched to demand the release of teenage students arrested for writing anti-government slogans on their school's walls. They were tortured in detention.
A report released a week ago by the international charity Save the Children said Syrian children are showing signs of "toxic stress" that can lead to lifelong health problems, struggles with addiction and mental disorders lasting into adulthood.
To cope with increasingly difficult living conditions, families inside Syria and in host nations have been forced to push their children into early marriages or child labour just to survive.
"There is so much more we can and should do to turn the tide for Syria's children," said Cappelaere.
The Syrian conflict began when the Baath regime, in power since 1963 and led by President Bashar al-Assad, responded with military force to peaceful protests demanding democratic reforms during the Arab Spring wave of uprisings, triggering an armed rebellion fueled by mass defections from the Syrian army.
According to independent monitors, hundreds of thousands of civilians have been killed in the war, mostly by the regime and its powerful allies, and millions have been displaced both inside and outside of Syria.
The brutal tactics pursued mainly by the regime, which have included the use of chemical weapons, sieges, mass executions and torture against civilians have led to war crimes investigations.
Agencies contributed to this report.