Three school children and the driver of their school bus were killed on Friday morning when a speeding jeep collided head-on with their vehicle in Hoshiarpur district of Punjab, police said.The victims died on the spot as the pick-up jeep, laden with potatoes, hit the driver's side of the school bus and virtually pierced through it. The accident took place on the Hajipur-Dasuya road.Among the dead were brother-sister twins and another student. All three belonged to Talwara town in Hoshiarpur district. The school bus driver, Ranjit Singh, also died in the accident.Other students travelling in the bus were injured. Six of them with serious injuries were admitted to a hospital in Dasuya town.The school bus was carrying around 15 children to the Gems Cambridge International School near Dasuya.Eyewitnesses told the police that the jeep, which was speeding, was trying to overtake another vehicle when it hit the school bus coming from the opposite direction.