Agence France-Presse reported mechanics heard moaning sounds and then discovered the little girl, who is between 15 and 23 months old, lying sick and dirty in the trunk. One of the mechanics, Guillaume Iguacel, said he was having trouble sleeping after seeing the girl surrounded by her own excrement.
Iguacel told the news wire he was disturbed that the 45-year-old woman, identified as Rose-Marie seemed unfazed by the baby's condition.
They called police, who told the news wire the mother had been hiding the baby from everyone since she was born, and even her father didn't know she existed.
The baby was dehydrated and hungry, and she had developmental delays, according to AFP. Her parents were both unemployed residents of the nearby village of Brignac.
Firefighters told Le Parisien the baby would have been in serious danger from lack of oxygen if she'd stayed in the trunk 15 to 30 minutes longer. One of the mother's neighbours told le Parisien the woman was always in her car.
The mother and father were arrested and they could face sentences of up to 10 years in prison, according to the London Daily Telegraph.
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