A group of 56 people is on trial in Paris accused of being part of a network that smuggled Bulgarian babies to French Roma (Gypsy) couples.
Many of the children are thought to have been born to prostitutes
Investigators believe that between 2001 and 2005 at least 22 children were bought by the couples, who were unable to adopt under French law.
They are said to have paid up to $10,000 for each child. The mothers were brought to France to give birth.
If found guilty the defendants face imprisonment and a fine.
Many of the children are thought to have been born to Bulgarian prostitutes.
Eleven of the defendants are suspected traffickers accused of bringing the birth mothers to France. They could be jailed for up to 11 years.
Another 41 are accused of buying the children and face up to three years' imprisonment. Two birth mothers and two suspected pimps are also on trial.
David-Olivier Kaminski, a lawyer for three of the couples, told AFP news agency the couples had been forced into a corner because France did not allow couples with roaming lifestyles to adopt children.
"These are French citizens, gypsies, desperate to have children, who had no hope of meeting these strict adoption criteria," he said.