"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.