The father and five children, aged 18 to 25, were found in the small village of Ruinerwold, in the northeastern province of Drenthe, Dutch police told CNN. A six-year-old child has left and alerted police.
Although the village has only a few thousand inhabitants, no one knew the family was there.
Police have arrested a 58-year-old man who rented a Property. Authorities say they are still trying to establish a bond between the detained man and the family and believe the family has been living there since 2010.
The investigation is ongoing
"It is not clear if they were left voluntarily again," the police statement said.
The family was not registered with government records. They have now been examined by doctors, police said.
"Part of our investigation is to find out exactly what the people in this house are doing. There are still many questions that we have no answer to. The investigation is still "People were taken to a shelter where they were cared for and where they would be asked to tell their story." , Police spokeswoman Natalie Schubart told RTL Netherlands.
Dutch police said they were found in a small room on the ground floor. Aerial photos of the property show a well-kept garden that looks like vegetables planted in neat rows, and NOS reports that the family also has a goat.
Aerial images of the property show three roofs. Some of the doors to the buildings are covered with overgrown greenery.
The home was accessible via a bridge over a river, which neighbors say has always been closed and locked, NOS reported. A neighbor told NOS that he once tried to get close, but turned back when he saw multiple cameras on the property.
"We understand that everyone still has a lot of questions. We have one," Dutch police said in a statement, adding that they had appointed a large team to investigate how the family got there and whether any crimes were committed.
A 58-year-old man has been arrested for failing to co-operate in the investigation, Dutch police said.
Rosanne Rubek, Stephanie Halash, Carly Wilson, Valeria Longy and Philip Victor contributed to the story.