Four persons were injured in the incident, they said.
"The passengers had boarded the auto-rickshaw in Rawatpur village at around 4.00 am. They were going to catch a train for Dewa Sharif, shrine of Sufi saint Haji Waris Ali, in Barabanki," Inspector Amar Singh of Kaant police station said.
Banna (50), Nazeeran (54) and Sunaya (9) died on the spot, he said.
Police said the truck driver is absconding.
The injured have been referred to Bareilly for treatment, they added.