Eight migrants, four of whom are children, children were found in a refrigerated lorry in France that was about to travel from the French port of Calais on the ferry to Britain, judicial sources said on Sunday.
The migrants, who said they were Afghans, were found suffering from light hypothermia in the lorry during a routine check at the port.
The French prosecutors have said the temperature inside the truck was around seven degrees Celsius.
The two drivers, both Romanians, have been detained, while the migrants were taken to a local hospital.
The discovery came after 39 people were found dead in a refrigerated truck in Britain this week, laying bare again the risks of illegal migrant routes to Europe.