Police in York, Pennsylvania, are asking themselves how the parents of five children aged two to 13 managed to conceal them for so many years with no birth certificates, no schooling, no vaccinations and no evidence of medical care – and why.

"I don't know what would possess them at all," said detective Dana Ward Junior, who tracked down the children after a child welfare agency received an anonymous tip-off. Ward has charged Louann Bowers, 33, and Sinhue Johnson, 45, with five counts of child endangerment. They are due to appear in court on Friday.

Years of isolation have taken their toll on the children, experts say. They are now living in foster homes, but "some suffer health and vision issues," Ward wrote in an affidavit. "None of the children are at their expected education levels, and there are possible mental health issues." They have now been vaccinated and the older ones enrolled in school.

Child and youth services became aware of the family through anonymous tips in 2003 and again in 2007, but police said Johnson refused to co-operate. The agency got another anonymous referral last year, this time from someone claiming to be a family member who had seen the children. Caseworkers obtained a court order to enter the family home. By the time they arrived, the family had fled.

Ward said it appeared that all seven of the family had lived in a single second-floor room. He said all the utilities were shut off. Rainwater came through the leaky roof and was collected in buckets.

Police tracked the family to a hotel outside York. Johnson had gone, but Bowers opened the door, her head concealed by a dark veil. The detective found the children, three girls and two boys, hiding in a bathroom. They were unwashed and appeared unkempt. They left with investigators without saying a word – and refused to provide any information.

"They did say that they were not permitted to talk about the family or the living conditions," Ward said.

The lack of co-operation from either the children or parents has stymied investigators' efforts to learn more about the family's circumstances.

The fact that almost no one knew about the children is even more puzzling because of where they lived. Neighbours say they never saw them, not even once.

Charlton Shaw, 56, a roofer who lives several doors away, said he was unaware of the children's existence until Johnson and Bowers were arrested. "I said, holy heck, how did they do that? You never heard a sound. No kids crying, no kids coming or going."