The attack is one of many carried out by Russian-backed regime forces throughout Syria over the past 24 hours.
Artillery fire began while the children were playing in the playground of the school in Harasta City.
Abu Zeyd, a rescue official at the scene, accused the regime of targeting civilians.
"These are only students and civilians, and it is all a nursery,” he said.
Adem added that the Hammuriyah neighbourhood of Damascus was also hit by regime warplanes.
The number of casualties from the attack is still unknown.
Meanwhile, Russian warplanes also targeted residential areas in northern Aleppo province according to official, Necip Ensari.
Video released by Smart News Agency, a Syrian media group based in Gaziantep, Turkey, quoted another rescue worker in the city who put the death toll in the Urum neighborhood attack at four and the number of wounded as high as 25.
Syria has been engulfed in a civil war for over five years that has seen the Syrian regime, led by Bashar al Assad, use deadly force to quell a national uprising inspired by the Arab Spring movement.
The country is currently split among regime-held areas, rebel-held areas and Daesh-controlled areas.
Over 5 million Syrians have fled their country since the conflict erupted in 2011. The International Organization for Migration (IOM) said about 21 percent of Syrians were living outside of their country by the end of 2015.