A member of the public raised concerns about the child living with the gypsy family in a house in a south Dublin suburb.
No arrests have been made and there is no allegation of abduction against the family.
The youngster was put into the care of the Health Service Executive (HSE) when the family were unable to prove her identity conclusively.
The couple have told police the girl, who they said was born in a Dublin hospital in April 2006, is their daughter.
They have several other children who have not been taken into care.
The youngster is said to be physically well and is due to be interviewed by specialist officers.
Unlike the case where a girl, known as Maria, was found in a gypsy settlement near Farsala in central Greece, DNA tests have yet to confirm the couple she was found with are not her parents.
Police are trying to establish the identity of the girl taken into care in Dublin and have contacted Europol and Interpol about missing children while investigations continue in Ireland.
It is understood officers may seek to take DNA samples from the parents and the child to fully determine whether they are her biological parents.
Police spent several hours at the property as they waited for documents to be produced.
A birth certificate was deemed to be inconclusive and a passport bore a picture of a baby and could not be matched to the seven-year-old.
The parents claimed the girl was born in the Coombe Hospital in Dublin, but when police contacted medical staff they had no record of a child with the family name being born on the date the parents claimed.
Meanwhile, Greece is holding an emergency nationwide fraud investigation into birth certificates sparked by the case of Maria. Supreme Court prosecutor Efterpi Koutzamani ordered the inquiry for certificates issued after January 1, 2008, amid reports of benefit fraud by families declaring births in multiple regions.
Experts have used the case to point out the severe weaknesses in the country's birth registration system.
The mayor of Athens has suspended three officials in charge of record-keeping. New parents have three months to declare the births. Investigators found many babies had been recently declared at or near the end of that deadline, raising suspicions some were multiple declarations to claim benefits.
A Roma couple are being held in custody charged with abduction and document fraud in the case of Maria. The girl, believed to be five or six, was taken into protective care last week after DNA tests established the couple were not her biological parents.
Christos Salis, 39, and Eleftheria Dimopoulou, 40, deny the abduction allegations, claiming they received the child from a destitute woman.