The death of a seven-year-old girl was discovered on Monday morning in the southern village of Sanilhac (Gard).
The girl's mother went to her bedroom at 7.30am to find her hanging from her bunk bed with a scarf around her neck, reported regional newspaper Midi Libre.
The girl was last seen alive the night before when her father read her a story at around 10.30pm. She had reportedly been having trouble sleeping.
The girl was due to go back to school on Monday, after a two-week holiday, although she was not believed to be worried about her return.
A second child was discovered dead in the southern Paris suburb of Villejuif on Monday.
The 12-year-old boy was also found hanging with a scarf around his neck.
Police were investigating both cases to discover whether they were accidents or incidents of the dangerous but popular "fainting game".
The "jeu du foulard", as it is known in France, involves strangulation to achieve a 'high' without drugs or alcohol.
22 children are believed to have died in France from this practice in 2010.