The accident occurred late last night near Kate village, police circle Khalilabad kotwali, when the private bus carrying pilgrims to an ashram in Mathura dashed into the truck which had come to a halt by the road after one of its tyres burst, police said.
Siblings, Satyam (12) Khushi (14), and Kusmawati (45) were killed on the spot, they said, adding, all the victims belong to Mahrajganj.
Six of the seriously injured have been referred to Gorakhpur Medical Collage Hospital while others are undergoing treatment in local hospitals.