You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
The five, estimated at 18 to 25 years of age, and a man they identified as their ailing father were found near Ruinerwold, a village in the northern province of Drenthe.
"We found six people living in a small space in the house which could be locked, not a cellar. It is unclear if they resided there voluntarily," local police said in a statement on Tuesday, adding that the people may have been hidden away on the property for nine years.
"They say they are a family, a father and five children."
Officials did not confirm local TV reports that the family may have held "end of days" apocalyptic beliefs.
Earlier, local Mayor Roger de Groot said a 58-year-old man, not the father of the children, had been arrested. His role was unclear.
The Dutch newspaper Algemeen Dagblad daily identified the man as "Joseph B.," an Austrian carpenter.
Police confirmed they had arrested a man who was renting the farm but would not comment on his identity.
The children's mother had apparently died before they moved to the Dutch farm, the mayor said. None of the family members were registered as residents with the municipality, police said.
The family, who according to local news reports had been waiting for the end of time, was discovered after one of the siblings escaped and sought help at a nearby cafe.
An employee at the cafe told RTV Drenthe one of the family members, a 25-year-old man with long hair, had come in looking scruffy and bewildered and said he had not been outside for nine years.
"You could see he had no idea where he was or what he was doing," the cafe owner, Chris Westerbeek, told the broadcaster. "He said he had run away and that he urgently needed help."
The siblings had apparently lived in makeshift rooms inside the farm and survived partly on vegetables and animals from a secluded garden on the property, local TV RTV Drenthe reported.
"I understand there are a lot of questions," De Groot said. "We have many too. The police are investigating all possible scenarios."