Two toddlers died of heat exhaustion when their fathers forgot they were strapped in child seats in the back of their cars as they went to work.

Both cases involve middle-class men, described as devoted and loving parents, who appear to have forgotten their children in an inexplicable lapse of concentration.

Prosecutors said yesterday that a three-year-old girl had died from heatstroke and dehydration after spending the day locked in her father's vehicle in the car park at the factory where he had a managerial post.

Jean-Louis Chapuis, the regional director of public security, said: “The parents were very attached to their children and they are not a family which is in difficulty. There is no objective way of explaining this drama except to say that it was a huge moment of forgetfulness, a mental lapse.”

The father, who has not been named, left home in the morning with Zoé, his daughter, in the baby seat in the rear of the car. Apparently unaware of her, he drove past the childminder 200m from his house in Saint-Marcel in eastern France, where she spent three days a week, and continued on to work. Police believe he may have thought that Zoé was spending the day with her mother. He parked the car at 9am and walked into his office at Areva, the French state nuclear operator.

The outside temperature was no more than 25C (77F), which is relatively low for southern France during the summer. Inside the car, it rose to 45C, according to fire officers.

At 4pm, the father got back into the car to fetch his five-year-old son from the town's nursery school - still apparently unaware that Zoé was in the baby seat. “He didn't even realise that the child was dead in the back of the car,” said a police source.

It was more than an hour later that he finally noticed his daughter. He drove directly to the local fire and ambulance station but rescue workers were unable to revive her.

“We have not been able to question the father. He is still in a very disturbed psychological state,” said Thierry Bas, the state prosecutor in nearby Chalon-sur-Saône.

Mr Bas said that Zoé had died three to five hours after being locked in the car. He said the father had been placed under arrest in hospital. Legal sources said he could be charged with manslaughter or with the offence of deliberately depriving a child of care.

The incident came seven days after a two-year-old boy died in similar circumstances in Pont-de-Chéruy, also in eastern France.

A passer-by found Yannis strapped into the baby seat in the family vehicle after being left for about three hours by Eric Allarousse, 38, his father. The outside temperature was between 25C and 27C. Mr Allarousse, who owns a chemist's, told detectives he had forgotten his son after witnessing a traffic accident after lunch on July 15.

Mr Allarousse spent the afternoon working in his chemist and only remembered about Yannis when he noticed fire officers trying to get into his car. “Yannis was his only child and he adored him,” said Jean-Louis Andreu, a local councillor. “Eric's profession meant that he was aware of the risks. Everyone here is totally shocked.” Prosecutors have yet to decide whether to bring criminal charges against Mr Allarousse.

Deadly temperatures

— Recent US studies found that the temperature inside a car parked in the sun could rise from between 20C (68F) and 25C to between 40C and 50C in an hour

— One study concluded that the interior colour of the car probably has the greatest effect on how quickly it heats up

— A child’s body warms three to five times faster than an adult’s

— The younger the child, the more vulnerable it is to heat exposure

— The average age of children to have died in cars in the US is 24 months

— Heatstroke occurs when the body’s core temperature reaches 40C. A body temperature of 41.7C is considered lethal

Sources: Pediatrics; Times research

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