Regime air strikes killed 12 civilians -- half of them children -- in Maaret al-Noman on Wednesday.
AFP photographers at the scene saw rescue teams working to pull people from the rubble after nightfall with the help of bright spotlights.
A rescue worker pulled a very young girl from the debris, her lifeless body covered in white dust.
Her bloodied head and little arm hung limp as he carried her in his arms to an ambulance.
Inside a morgue, a young father sobbed over the bodies of his three dead children and their cousin, none of whom appeared older than five.
Also on Wednesday, another four civilians, including one child, were killed in other parts of the bastion.
Increased bombardment by the Syrian military and Russia since late April has killed more than 950 civilians in Idlib.
In the same period, the violence has displaced more than 400,000 people including many already uprooted from other areas, the United Nations says.
The bombardment and ground offensive come despite a deal between Russia and rebel backer Turkey in September last year to protect the area with a planned buffer zone.