"My clients will appeal against their detention," lawyer Marietta Palavra told AFP.
"They also want the child back as they are the ones who have raised her and they love her," she added.
Fair-skinned Maria was found living with a Greek Roma couple in a camp near the central town of Farsala on October 16, sparking global news interest and hundreds of enquiries from parents of missing children.
They were arrested and placed in prison this week pending trial.
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Instead, DNA tests yesterday confirmed that Maria's biological parents are Sasha and Atanas Rusev, a Bulgarian Roma couple living in dire poverty in the town of Nikolaevo in central Bulgaria.
Sasha Ruseva, 35, told police that she had given birth to a baby girl while working in Greece several years ago and left her there when she was seven months old.
She said lack of any identification documents for the baby as well as poverty and inability to take care of her many children had prompted her to abandon the child and return to Bulgaria.
"They recognise Ruseva" as the woman who gave them the child, Palavra said.
"They feel vindicated because this is the story they have told from the start," she said.
Both Ruseva and the Greek Roma couple insist no money changed hands.
Maria is currently in the care of Smile of the Child, an Athens-based charity.
Ruseva had earlier declared that she was ready to take Maria back if DNA tests confirmed that she was her real mother.