A train crushed two motorised rickshaws on an ungated crossing, killing seven schoolchildren in Punjab's Lodhran district, police said.
Police officer Javed Ahmed said the rickshaw drivers apparently misjudged the speed of the coming train due to heavy fog while attempting to cross the tracks early Friday morning near Lodhran.
The train was heading to Karachi from Lahore.
Ahmed said another five children aged 5 to 8 years and one rickshaw driver were critically injured.
Train accidents are common in Pakistan, which inherited thousands of kilometres of track and trains from former colonial power, Britain.
The railways have seen decades of decline due to corruption, mismanagement and lack of investment.