The two girls, called Charline and Julie, were found in the town of la Flèche, 40 kilometres south west of Le Mans in the west of the country, 17 hours after they had disappeared.
They were discovered in a station car park, reportedly in tears, by two women. After being interviewed by police they were taken to the hospital in Le Mans for tests where they spent the night.
The girls' disappearance took place at around 9pm on Saturday evening after the older girl, Charline, "asked her mother's permission to go for a walk with a couple the girls had met in a local playground," according to a police spokesman. They had apparently got to know the couple recently and had been playing with their young baby.
The mother gave her permission, while asking them not to come home too late.
"I am relieved, tired," the girls' father, Marc Chapin, told journalists on Sunday evening after hearing his daughters were safe. "I'm told the girls are fine and they are in the hands of a psychologist."
Police attention has now shifted to the couple who are alleged to have kidnapped the girls on Saturday. They are described as a young couple with a white van registered in the Sarthe area in which they disappeared and are travelling with their 18-month-old child.