The identities of the deceased could not be known immediately.
The accident took place on the Dhaka-Sylhet highway at 12 noon when a bus of 'Saudia Paribahan' hit the pedestrians.
Mother and son died on the spot and two others were taken to upazila health complex in critical condition, reports BSS.
Officer-in-Charge (OC) of Sherpur Highway Police Station Abu Taher Dewan confirmed the matter.