The six members of L'Arche de Zoe (Zoe's Ark) returned to France on Friday, two days after a court in Ndjamena, the capital, sentenced them to eight years of hard labour on charges of trying to abduct the children.
The Chadian government had agreed to a French request that the six serve their sentences in France.
However, the French justice system could reduce their sentences, as French law does allow for forced labour of prisoners.
On arrival in Paris, the six were taken to a prison in Fresnes, outside the capital.
Family members visiting the charity workers for the first time said two of the six - Nadia Merimi and Eric Breteau, the head of Zoe's Ark - were hospitalised at the prison.
Breteau is said to be "very sick".
The French nationals were arrested in October as they tried to fly the children, aged one to 10, to Europe for fostering with families.
Zoe's Ark had said it was helping to rescue orphans from Sudan's war-torn Darfur region across Chad's eastern border.
But most of the 103 children were found to have come from families in Chadian border villages who were persuaded to give up the infants with promises of education at local centres.
Lawyers for the aid workers later said intermediaries had tricked the charity into taking the children when they had genuinely believed they were rescuing Darfur orphans.