A family drove for more than 90 miles (about 150km) before realising they had left their three-year-old daughter at a motorway lay-by.
The French couple said they only realised their daughter was missing after hearing an alert issued by French radio.
The toddler was discovered by holidaymakers on Sunday at the motorway rest-stop just off the A7 “Autoroute du Soleil” in southern France.
According to local authorities, the girl told the people who found her that she had a brother and a sister and she was “going to the seaside” when she saw “daddy's car pull away”.
It was only 45 minutes later when the girl's parents were nearing the coast that they heard the police alert, realised their error and turned back towards the site near Loriol, in the Drôme region.
“The family had passed Aix-en-Provence [150km away] and were going towards Saint-Raphaël and none of them had noticed she wasn't there,” said a French police officer.
The parents were being questioned on Sunday evening by officers at the police station where the child was being looked after.
“We are going to listen to what they have to say and talk to the prosecutor at Valence to see if this should be taken further,” the officer added.
Millions of French families take to the roads during August's annual holiday rush to the sea and mountains, putting often unbearable strain on the country's motorway system.
The Independent