Boonnam Dussadee rushed his wife Sutthida Sakul-eiw and son to Paolo Memorial Chaokchai 4 Hospital after he found them unconscious in the car at about 9.30pm – but they were already dead.
Boonnam ate with friends at the restaurant for about an hour while the wife and son waited in the car.
There was no sign of a struggle in the car and the bodies had no wounds, said Chokchai Police Station superintendent Colonel Chairop Junnawat yesterday.
The car in which the mother and son died will be checked to see if a malfunction caused their deaths.