Activists in Syria say a government jet has dropped a cluster bomb on a playground, leaving 10 children dead.
Video posted on the internet showed children's bodies on the ground with their mothers grieving over them.
The children were killed when a MiG fighter bombed a playground in the village of Deir al-Asafir, east of Damascus, opposition activists said.
Intensive fighting has continued around the capital. Rebel fighters captured at least part of an airbase on Sunday.
Further footage of the playground attack showed what appeared to be cluster bomblets on the ground. In one video, two girls could be seen lying dead in a street while another showed a distraught mother standing, apparently inside a clinic, over her daughter's lifeless body.
In recent months there have been mounting allegations that the Syrian government has resorted to using cluster bombs as the conflict intensifies, although those claims have been denied, the BBC's Jim Muir in neighbouring Lebanon reports.
Two cluster bombs were dropped on the village, activists said. One man told Reuters news agency that 70 bomblets had been found.
"None of those killed was older than 15 years old," Abu Kassem, an activist in Deir al-Asafir told Reuters.
He said 15 people had been wounded in the attack and denied that rebel fighters were inside the village. They had been operating on the outskirts, he said.
Last month, Human Rights Watch said there had been an increase in online video reports purporting to show evidence of cluster bombs being dropped in the conflict, especially around the town of Maarat al-Numan.
Damascus said the army did not have such weapons and dismissed the allegations as "baseless".
An unverified report by activist group Local Co-ordination Committees put the number of casualties across Syria on Sunday at 117, including 14 children.
Rebel fighters said on Sunday they had captured a military airbase at Marj al-Sultan although activists of the UK-based Syrian Observatory for Human Rights said they had later pulled out.
Amateur video showed a rebel standing beside a wrecked helicopter while a man speaking on the video said a warplane had been blown up.
1. Cluster bombs are usually dropped from a plane and can fly several miles before releasing their load of bomblets.
2. The canister starts to spin and opens at an altitude between 1,000m and 100m, spraying the bomblets across a wide area.
3. Each bomblet is the size of a drink can and contains hundreds of metal pieces. When it explodes, it can cause deadly injuries up to 25m away.