Sudan's minister for social affairs, Samia Ahmed Mohamed, said 18 of the children were Sudanese.
N'Djamena had still not agreed to return six from a holding camp in the east of Chad and she said she feared for their safety.
"A group of Sudanese lawyers will bring charges against the kidnappers for a crime they were not tried for -- child trafficking," she said.
The six from the Zoe's Ark organisation were sentenced to eight years' hard labour by a Chadian court last year and were allowed to serve their sentences in France. On Monday, Chadian President Idriss Deby pardoned them and they were released.
Sudan will ask Interpol to post arrest warrants for the six French nationals and compensation will be sought for the families of the Sudanese. "I am very astonished ... at the release of the criminals," Mohamed said.
"It is clear that the trial was a sham and there was a deal between the two countries and the victims were the children."
France has a policy of not extraditing its own citizens. Several members of the group have been placed under formal investigation in France for fraud and other charges, making it unlikely that Sudan's warrant would lead to an arrest.
Mohamed urged the United Nations to intervene to release the six Sudanese in a holding camp in eastern Chad.
The other 12 Sudanese children were returned to their families who had fled to eastern Chad during the war. The six still in Chadian care were originally taken from West Darfur.
The minister accused Chad of using the children as a tool in the deteriorating relations between the two neighbours.
"Chad is taking the children as part of the political machinations between the two countries and are using them as if they are hostages," she said.
Last Mod: 03 Nisan 2008, 09:01