The train reportedly crashed into a tree that had been left on the tracks following a heavy thunderstorm near Montpellier, leaving 11 people seriously injured.
The teenagers, attending an open camp near Strasbourg, were evacuated to a nearby arena just minutes before fierce winds damaged the site.
Court said mayor knew of flooding risks but hid them to allow seaside homes to be built; 29 died in 2010 storm when sea wall broke.
Winds of up to 120km/h swept parts of the country, cutting power mainly in the Loire Valley in the west, but also Normandy in the north-west.
Cargo vessel slams into dyke after 'complete electrical breakdown' in high winds and strong seas off Anglet near Bayonne on Atlantic coast.
The body has been found of a 47-year-old woman washed out to sea off the Brittany island of Belle-Île amid strong storms across northern France.
France, Britain, Ireland and the Benelux countries are threatened by a major storm sweeping over the Atlantic and which threatens severe damage.