The Syrian Observatory for Human Rights said "seven rockets and several shells hit areas on the edges of Qabun", a northeastern district of Damascus held by rebels.
"The shelling targeted a cemetery while someone was being buried there," said Observatory head Rami Abdel Rahman.
"The toll may increase because there are about 15 people wounded, some of them in critical condition," he said.
Rebels and regime forces reached a local truce deal in Qabun in 2014, but violence steadily escalated in the neighbourhood which is now bombarded regularly.
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The Observatory said two young brothers were among the dead.
The toll brought to 30, including 10 children, the total number of people killed in an "escalating air campaign and clashes in Waer", Abdel Rahman told AFP.
Homs was dubbed the "capital of the revolution" after vast demonstrations there early in Syria's anti-regime uprising.
But after months of siege and bombardment, rebels agreed to quit the city in a 2014 evacuation deal with the government.
Another local deal was struck specifically for Waer in December 2015, and hundreds of rebels have left the neighbourhood.
But after nearly six years, the conflict has morphed into a multi-front war that has drawn in foreign powers and seen jihadist groups rise to prominence.