They had not permitted social interaction, although it was unclear whether the child was kept permanently indoors, the lawyer added.

Social services took charge of the girl July 15 and brought her to a clinic after a neighbour reported the case, a regional government spokeswoman said.

The girl appears to have been kept isolated since her parents moved nine years ago to the small town of Luebbenow, 100 km north of Berlin. People in the town knew however that she lived in the house, Schiermeyer said.

The girl has two siblings, who are also being looked after by the local youth services.

The education ministry of the state of Brandenburg is also investigating how the parents could avoid sending the girl to school.