Young migrants are being hidden and sheltered by French villagers near the Italian border, who sometimes help them to slip undetected into the country.
At least 150 residents of several villages in the Roya valley, northeast of the French Riviera coast, have taken African and Middle Eastern teenagers into their homes "for humanitarian reasons", local sources said.
Police arrested more than 36,000 migrants in the area last year, most of whom were sent back to Italy, prompting local people to form a support group called "Roya Citizenship".
One woman, identified only by the first name Sophie, said she had given shelter to two teenagers from Eritrea at her home in Saorge. "If the police come, I'll say they're underage," she told the newspaper Le Parisien.
Many of the migrants in the area hope to settle in Britain where they say they have relatives or friends.
In a landmark judgment, a university professor from Nice who was arrested with three Eritrean women in his car was cleared of aiding illegal immigration on Friday. The court ruled that he had acted "to help persons in distress". Pierre-Alain Mannoni, 45, said he was taking the women to spend a night at his home and then planned to drive them to a railway station.
Cedric Herrou, 37, a farmer from the village of Breil-sur-Roya has been charged with helping dozens of illegal immigrants cross the border from Italy. A court is to rule next month.
Hundreds of migrants have reportedly returned to the Calais area since the "Jungle" camp was closed in October.