Seven of those killed in regime and Russian strikes in Sarmeen town of Idlib province were all members of one family, Syrian Observatory for Human Rights says.
Air strikes by the regime and its Russian ally on Sunday killed at least nine civilians in the last major opposition bastion of Idlib in northwestern Syria, a Britain-based war monitor said.
The Syrian Observatory for Human Rights said seven of those killed were all members of one family in the town of Sarmeen in Idlib province.
A correspondent of AFP news agency saw a man weeping as rescue workers pulled bodies from a crumpled two-storey building.
They belonged to his nine-year-old daughter and a 13-year-old son.
A regime air strike also killed a child in the town of Binnish, and a Russian raid took the life of a woman in the town of Atareb, the Observatory said.
The Russian-backed regime and militant forces are advancing on the rebel-held town of Saraqeb amid a double-pronged push into Idlib province, home to some three million people, half of whom have been displaced from other parts of the country.
The fighting in Idlib and in western Aleppo over the past week has killed 205 pro-regime militants and 220 anti-regime combatants, the SOHR said.
UNICEF said Saturday that violence this week forced 6,500 children to flee daily, bringing the total number of displaced children in northwest Syria to more than 300,000 since early December.
The regime of Bashar al Assad, which controls more than 70 percent of Syria, has repeatedly vowed to reclaim the entire country, including volatile Idlib.
Both the Syrian regime and its Russian ally, whose air power has been critical to Damascus' military gains in recent years, deny targeting civilians or civilian infrastructure.
The war in Syria has killed more than 400,000 people and displaced millions since it started in 2011 with a brutal crackdown on anti-regime protests.