The source also said the group had begun the protest because they felt that no one was listening to their case, that they had been abandoned by the French government and that a Chadian official involved in the case had not been arrested.
He also said it had been decided that the trial of the six, who face charges of fraud and abduction and could be sentenced to forced labour terms if convicted, would be held in Chad and that it would start in the coming weeks.
Neither lawyers for the French nationals nor Chadian court officials were immediately available to comment.
Zoe's Ark had said it wanted to fly orphans from Sudan's Darfur region to Europe for fostering by families but UN officials who questioned the children said most were not orphans and came from villages on the Chad-Sudan border.
The seven-member Spanish crew of a chartered plane, three French journalists and a Belgian pilot arrested with the group were later released after Nicolas Sarkozy, the French president, flew to Chad to discuss the case with Idriss Deby, his Chadian counterpart.
France has strongly condemned the Zoe's Ark operation but the case has strained relations with its former colony ahead of the planned deployment of an EU peacekeeping force in Chad's restive east.