WASHINGTON (DPA) - A federal judge has approved a US$3 million (S$4 million) settlement for three children who were molested after a Washington state adoption caseworker placed a sexually aggressive 12-year-old boy diagnosed as a "psychopath" into their home without telling the family.

That amount is on top of US$4.8 million awarded to the Island County parents of the children by a state court jury in January 2017 after finding the Department of Social and Health Services (DSHS) negligent in its decision in 2013 to adopt into their home a violent and deeply troubled boy identified in court documents by the initials WS.

According to those documents, WS has since been convicted in juvenile court of molesting the other children in the home, ages 12, six and five at the time, and is a registered sex offender. One of those children was also an adopted foster child.

The US$3 million settlement, approved by US District Judge Richard Jones, will be divided between the three children and the family's attorneys, Connelly Law Offices, according to the documents.

The lawsuit alleged that WS' DSHS caseworker, Katherine Graff, had explained that WS suffered from a series of emotional problems that included acting out and physical violence, but did not disclose that a previous caseworker had documented extremely aggressive sexual behaviour by the child and had recommended a "sexually aggressive youth" evaluation.

Moreover, according to pleadings in the lawsuit, Graff in February 2013 was provided with information from a neuropsychologist that the boy was a potentially dangerous psychopath, but placed him in the family's home in April without passing on the information. The civil rights lawsuit alleged Graff acted with deliberate indifference by placing WS into the home without adequately warning the family.

DSHS, in a motion to dismiss the lawsuit, argued that Graff provided the family with a wealth of information about the boy's emotional problems and had been trying to place him in a residential home where he would receive treatment.

However, the family did not want that for him and asked to have the boy placed with them as a foster child in 2012 even after being told that he was violent, according to the DSHS pleadings. Despite this information, DSHS said, the family went ahead with adopting the boy.

Assistant Attorney-General Kerri Anne Jorgensen, who represented Graff and DSHS in the lawsuit, declined to comment. Debra Johnson, the director of communications for the newly formed Department of Children, Youth and Families, said the agency "intends to provide improved quality care (for) the children we serve by improving how we operate this agency".

"In this case, we hope this settlement provides resources to help the children recover from a traumatic time in their lives," she said.

The family - whose name is being withheld by The Seattle Times to protect the identity of the child victims - discovered the abuse when they caught WS "humping" one of the younger children on a family trampoline. An investigation revealed all three children had been sexually abused or assaulted by WS.

An aunt of the boy later told the family that she had tried to adopt him but had given him up because of "his violent behaviours and lack of remorse when hurting his younger siblings".