The incident occurred on Sunday night near Falsund town when the driver of the truck turned to take a short route to Baytu and crushed the victims who were sleeping by the road side, police said.
The minor died on the spot while her father Ramesh and grandfather Shankar succumbed to injuries in hospital, they said.
The truck has been seized and the driver is absconding, they said.
Defence PRO said a Court of Inquiry has been ordered to ascertain facts of the incident.