The boy’s 45-year-old father, a triathlete from the canton of Bern, has yet to be found after searchers discovered the Renault in a stream bed on Sunday, Italian media reported.
The accident occurred on Saturday night as the boy and his parents were returning to a holiday home on a farm, where they were vacationing with a group of around 20 triathletes in the Italian region.
The boy’s 43-year-old mother got out of the car to walk to the holiday home, at the suggestion of her husband, while he parked the car, the Italian press agency Ansa said, citing information released by local authorities.
A torrent of water subsequently carried the car away, Ansa said.
Tuscany, in particular, the southern part of the Italian region, was hit by heavy rain and flooding over the weekend.
Fire fighters, divers and search dogs were engaged in the search for the missing pair on Sunday and on Monday.
The boy’s mother was able to return to the holiday home on foot.
She was unhurt but remains “in shock” and is receiving psychological counselling, Ansa reported.
The car was just 150 metres from the road, stuck under the arches of a small bridge, but the boy’s body was found seven kilometres away, Italian newspaper La Nazione said.
Inside, the vehicle was empty except for the boy’s backpack and a few coloured pencils, farmer Piero Bondi, who pulled out the car with a tractor, told the newspaper.
Divers also found a windbreaker and sweat shirt belonging to the boy’s father, according to reports.