The woman and her children were killed when a homemade rocket fired from the rebel-held east of the city hit their home around midnight in the Ashrafiyeh district, the Observatory said.
The Britain-based monitor said rebels were firing homemade explosive devices often using gas canisters that were even more damaging than regular mortar fire.
Aleppo, Syria’s second city and former industrial powerhouse, has been divided between rebel control in the east and regime control in the west since shortly after fighting began there in mid-2012.
Since the end of 2013, the Syrian air force has regularly dropped explosive-packed “barrel bombs,” which rights groups criticise as particularly indiscriminate, on the rebel east and surrounding province.
The barrel bomb attacks have killed several thousand people in Aleppo province, according to the Observatory.
In recent months, rebels have intensified their mortar attacks on the government-held west of the city, killing nearly 300 people in four months, the group said. (AFP)