Emergency services last night rushed to the scene in Immingham, Lincolnshire, at 9.06pm.
Cops say a white articulated lorry was travelling westbound along the A180 when it collided with stationary blue Ford Focus which is thought to have broken down in a live lane.
A Humberside Police spokesperson said: “Sadly, a 34-year-old woman and 3-year-old boy travelling in the Ford Focus sustained fatal injuries as a result of the collision and died at the scene.
Their families have been informed and are currently being supported by specialist trained officers and partnering agencies at this incredibly difficult time.
We are appealing for anyone who may have dash cam footage or who witnessed the collision to contact us on our non-emergency number 101 quoting log 557 of 10 March.