Most of the deaths were reported from southern Punjab, as temperatures shot up to 47 degrees Celsius in Multan and 48 degrees in Dera Ghazi Khan and Bahawalpur.
More than 150 people also fainted due to the sizzling heat, the newspaper said.
The three children died Sunday and 50 people, most of them children, were admitted to hospital in Sheikhupura.
The number of gastroenteritis cases in the district has touched 1,200 within a month and the death toll stood at 11.
Muhammad Azhar Hayat, the medical superintendent of Sheikhupura DHQ hospital, said that water contamination was the reason for the increasing incidence of gastroenteritis in the area.
Around 50 people were admitted to government and private hospitals in Daska and Sambrial Tehsils Sunday.