The Oxford Research Group, which specialises in global security, said in a new study that there were 11,420 recorded deaths of children aged 17 years and under.
The report, entitled "Stolen Futures: The hidden toll of child casualties in Syria", analyses data from the beginning of the conflict in March 2011 until August 2013.
The think-tank added that, of the 10,586 children whose cause of death was recorded, 128 were killed by chemical weapons in Ghouta, near Damascus, on August 21,2013, in an attack that the United States and other world powers blamed on President Bashar al-Assad's regime.
The think-tank added today that 764 children were summarily executed and 389 were killed by sniper fire in the conflict.
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Explosive weapons have caused more than 70 per cent of the child deaths, while small arms fire accounts for more than a quarter, according to the study.
"What is most disturbing about the findings of this report is not only the sheer numbers of children killed in this conflict, but the way they are being killed," said report co-author Hamit Dardagan.
"All conflict parties need to take responsibility for the protection of children, and ultimately find a peaceful solution for the war itself."
Oxford Research Group added that the number of boys killed outnumbered girls killed by a ratio of about two to one.
Those children in older age groups were targeted more often than younger children. Boys aged between 13-17 years old were the most frequent victims of targeted killings.
"The world needs to take a much closer interest in the effects of the conflict on Syria's children.