Naugachchia Superintendent of Police Rakesh Kumar said the incident happened when the four were standing near the bus stand.
A few trucks were also parked along the roadside.
The accident occurred when one of the trucks, parked along the road, jumped the queue due to which another truck parked behind it lost balance, skidded and fell over the four persons standing close by, the SP said.
The victims have been identified as Bhola Yadav (22), his sister Kiran Devi (28) and her two children.
They were residents of Toufil Diara (riverine area) under Kahalgaon sub-division.
Police officials said Bhola and Kiran were identified with the help of locals, as well as with their names tattooed on their forearms.
The driver of the truck escaped, while its conductor has been arrested.
