Panagiotis Pardalis, a spokesman for the Smile of the Child charity, said Tuesday the reports were "being taken very seriously," CNN reported.
Pardalis said the reports included children missing from the United States, Canada, Poland and France.
Greek police have charged a Roma couple with kidnapping a blonde girl believed to be 5 or 6 years old authorities are calling "Maria."
A lawyer for the couple said they adopted the girl from her biological mother.
Police say they are suspicious of records provided by the couple. The birth certificate for the girl was issued only this year.
The head of the agency from which "Maria" got her birth certificate has been suspended along with three other officials while the investigation is under way, said the Athens municipal media office.
Questions about the girl were raised because her parents have darker complexions typical of Roma, or gypsies. DNA testing has confirmed they are not her biological parents.
In a separate incident, Irish police raided a Roma home in a Dublin suburb and removed a 7-year-old blonde, blue-eyed girl, CBS News reported.
The family could not initially provide a birth certificate for the girl, but later claimed she was born in a hospital in Dublin in 2006. Hospital officials said they had no record of the birth.
Police took custody of the child after they determined documents that were eventually produced were inconclusive.