The fighting in Nabak pits Assad's army and allied militia against rebel factions including two linked to al Qaeda, the Nusra Front and the Islamic State of Iraq and the Levant.
The Syrian Observatory for Human Rights, a British-based pro-opposition monitoring group, said five children were killed when pro-Assad forces entered Nabak's industrial area.
Activists posted images on social media of the bloodied corpses of five children and said up to seven had been killed. Some blamed a Shi'ite militia for the killings, but this could not be confirmed.
The rebels are mostly Sunni Muslims.
"What we know is that they (the children) were killed by shooting," Rami Abdulrahman, the Observatory's director, said.
The report could not be independently verified.
Nabak lies 80 km (50 miles) north of Damascus on Syria's north-south highway linking the capital to the central city of Homs and the coastal heartland of Assad's minority Alawite sect.
Fighting in the area intensified last month when the government launched an offensive to secure towns along the road.
The Observatory said pro-government forces shelled the eastern areas of Nabak and raided homes in the western areas.