For years, two French couples had doubts over whether their daughters were really theirs and a DNA test eventually confirmed their worst fears, revealing the girls were switched at birth.

On Tuesday, the families of the girls now aged 20 were in court in the southeastern city of Grasse, suing doctors and the clinic involved in the case for more than 12 million euros ($15 million) in damages.

The story began in July 1994, when Sophie Serrano gave birth to little Manon at a clinic in the French Riviera resort of Cannes, near Grasse.

The baby suffered from jaundice and doctors put her in an incubator equipped with lights to treat the problem along with another affected newborn girl.

An auxiliary nurse unwittingly switched them, and while both mothers immediately expressed doubt about the babies, pointing to their different hair lengths, they were sent home anyway.

Ten years later, troubled by the fact his daughter bore no resemblance to him with her darker skin, Manon's father did a paternity test that revealed he was not her biological parent.

Sophie Serrano then discovered she was not Manon's mother either, prompting a probe to try and find the other family who had been handed their biological daughter.

The investigation revealed that at the time of the births in 1994, three newborns suffered from jaundice — the two girls and a boy — and the clinic only had two incubators with the special lights.

The girls were therefore put together in one incubator, according to the lawyer of one of the obstetricians being sued.

Another obstetrician, two pediatricians, the clinic and an auxiliary nurse are also being sued.

The two sets of parents eventually met their biological daughters for the first time when they were both 10 years old, but did not ask that they be switched back.

Ten years later, both families are suing for a total of more than 12 million euros.

The other family involved in the case also attended Tuesday's closed-doors court hearing but opted to remain anonymous.