The Syrian Observatory for Human Rights said the six members of one family died in the rebel-held area of Dael.
All of the children were under the age of 18.
Two brothers and another relative were killed in another house in the same air attack, the Britain-based group said.
It said a regime barrel bomb attack in the Al-Karak al-Sharqi area killed six people in the same family, including three women and a child, as well as a couple.
Two more civilians died in raids on the rebel-held area of Tafas.
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"The regime has intensified its air campaign after losing ground in Daraa province in recent months," Observatory chief Rami Abdel Rahman said.
It was in Daraa that peaceful demonstrations broke out against President Bashar al-Assad's regime, prompting a harsh crackdown that led to armed rebellion.
"The regime is trying to make up for its losses, but is bombarding houses where there are women and children," Abdel Rahman said.
Rebels have gained two significant victories over the army by taking the main border crossing point with Jordan and the ancient town of Bosra al-Sham.
In the northeast, regime forces have also lost Idlib city, the second provincial capital to fall to the insurgency in four years.
Analysts say the rebels' main backers Saudi Arabia, Turkey and Qatar have set aside their differences and supplied the insurgency with more weapons to halt regime advances and curb the influence of Damascus ally Iran.