The sand laden dumper coming from opposite direction collided with the motorcycle killing all four on the spot, a police official said.
The deceased have been identified as SK Saiful (26), his married sister Ismatara (25) and her two children Aslam Mollah (8) and Amina Khatun (5).
Ismatara, along with her two children was returning to her in-laws after Eid celebrations at her father's house, the official said.
The dumper was set on fire by a mob and its driver was later arrested, they said.
Disclaimer: No Business Standard Journalist was involved in creation of this content