Speaking to reporters on Sunday, Foucher said: "This is a completely illegal operation. The members of Children Rescue who took part in this entire illegal manipulation will [be] held accountable for their actions in Chad."
Nine French nationals - six members of the operation and three journalists - as well as the seven Spanish crew members of the chartered aircraft are in custody in Abeche, and were expected to be informed of the charges against them by Monday.
Idriss Deby, the Chadian president, has promised "severe punishment" for what he describes as a "kidnapping" or "child trafficking" operation, suggesting the group were seeking to sell the children or "kill them and remove their organs".
Zoe's Ark representatives in Paris say they mounted the "Children Rescue" operation in good faith, hoping to evacuate a group of orphans whose lives were at risk in Sudan's war-torn region of Darfur, over the Chadian border.
The charity insists it was given statements from local tribal leaders that all the children were Darfur orphans with no known relatives. A Belgian pilot who flew the children as far as Abeche said the Chadians were aware of the operation, which the government denies.
But children's charity Unicef said after interviewing the children - 88 boys and 22 girls, all in good health - that most appear to be Chadian, not Darfuri, and that there was no evidence they were orphans.
The botched operation has sparked deep concern in France, where the children were reportedly to be adopted or fostered by families who each paid 2,800-6,000 euros ($4,000-8,600), allegedly to cover evacuation costs.
France condemned the operation as "illegal" and "irresponsible", saying it warned Zoe's Ark months ago that it risked breaking the law. French police have been investigating the charity's activities since July.
Marie-Roger Biloa, the founder and editor of Africa International magazine, told Al Jazeera that some organisations believe that they can go to Africa and grab children when they are in trouble.
Biloa said: "When the proper procedures are followed, and the parents agree to the children being taken away, the process can move forward. But in this case, some of the parents did not agree."
Bernard Kouchner, the French foreign minister, telephoned Deby on Saturday to assure him of his "solidarity" with the children and has set up a crisis cell to monitor the "humanitarian consequences of the operation".
Aid groups working in eastern Chad, home to 236,000 cross-border refugees from Darfur as well as 173,000 people displaced by local fighting, have firmly condemned the operation.
Zoe's Ark, whose members were granted access to French military aircraft and facilities in Chad, says the French government was aware of its plans and did not try to stop them.
The charity was founded by Eric Breteau, a volunteer firefighter and among those arrested in Chad, to provide assistance to victims of the December 2004 Asian tsunami.
The Children Rescue operation initially planned to fly 10,000 children out of Darfur to Europe, a plan denounced as "irresponsible" and amateurish by adoption and humanitarian groups.
One would-be adoptive parent, Guillemette Faure, told AFP news agency that she contacted Zoe's Ark but was scared off by a "blurring of lines between fostering and adoption" and the lack of guarantees the children were orphans.
But she said she was "uncomfortable" to hear the group described as "child traffickers".