Syrian army helicopter fire killed nine children in a camp for displaced civilians near the Jordanian border on Wednesday, a monitoring group said.
They were among 12 civilians killed in the air raid on the camp near the village of Shajara, south of Damascus, the Syrian Observatory for Human Rights said.
The youngest of those killed was a girl aged just four, the Britain-based group said, adding that seven people were also wounded, three of them women.
"The victims were all civilians, people who had fled the violence in other parts of Daraa province," Observatory director Rami Abdel Rahman told AFP.
The air raid comes amid escalating violence in Daraa province, where rebels have been advancing in recent months, according to activists.
Nearly half of Syria's population has fled their homes since the uprising against President Bashar al-Assad's rule erupted in March 2011.
More than three million have found refuge abroad.
But around six million more are displaced inside Syria, with many living in terrible conditions in camps along the borders.
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On Tuesday night, Syrian government aircraft also bombarded several rebel-held areas of Aleppo province in the north, keeping up an aerial offensive that has killed some 2,000 people, including more than 500 children, since January, according to the Observatory.
The army fired two surface-to-surface missiles at the Waar district of Homs, the only area of the central city still under opposition control, activists reported.
Rebels pulled out of the Old City of Homs under a UN-brokered deal in May, after spending two years under army siege.
The missile fire came as negotiations for a truce in Waar on the outskirts of Syria's third city stalled despite hopes raised by the May agreement.
The Observatory meanwhile expressed concern over the fate of 145 Syrian Kurdish children kidnapped late last month by the Islamic State of Iraq and the Levant (ISIL), the same feared jihadist group which has spearheaded the seizure of a swathe of neighbouring Iraq over the past week.
"Residents and some of the students' families in the town of Ain al-Arab told the Observatory they are very worried that ISIL may forcibly recruit the children and make them carry out suicide attacks using vehicles or explosive belts," the Observatory said.
The town, known as Kobani in Kurdish, lies on the central part of Syria's northern border with Turkey and is one of three mainly Kurdish areas of Syria where Kurdish leaders want to establish an autonomous region.
But Kurdish militia have faced repeated attack by ISIL, particularly in the mainly Kurdish northeast, where the jihadists have their own ambitions to link up with their fellow fighters in Iraq.