The attack took place on Friday morning in the city of Jisr al-Shughur. The children were siblings and under the age of ten, according to SOHR. The victims were internally displaced persons from Hama province.
In April, four children were killed in an airstrike in a nearby village.
Russia supports President Bashar al-Assad in the war in northern Syria. Parts of Idlib province are controlled by various rebel groups fighting the regime in Damascus.