After five-year-old Harmony Montgomery went missing in 2019, questions surfaced about whether the state did enough to protect her. Now, the adoptive fathers of Harmony's brother say the system failed, and they're pushing for change.

Johnathan Bobbitt-Miller and Blair Miller adopted Harmony's brother Jamison, who is six. They said on Greater Boston that Jamison asks about Harmony often.

"It is very difficult to answer his questions. He looks at us and says, 'Why did my sister have to die? Why did someone have to hurt my sister?'" Bobbitt-Miller said. "That was the only stable person in his life until he was adopted."

Blair Miller said state agencies and lawmakers should implement improvements to make sure such a case doesn't happen again, but they haven't.

"Why hasn't enough changed to make sure this doesn't happen again?" Miller asked.

Harmony is presumed dead and her father, Adam Montgomery, has been charged with her murder. Harmony had stayed in the care of her father despite signs of abuse. A new report from the Office of the Child Advocate says the state is not adequately protecting kids in custody cases.

Retired Judge Carol Erskine, who aided in Jamison's adoption and is writing a book about Harmony's case, said one change could come from a Massachusetts law that lets children decide where they want to stay.

Harmony, at just four years old, said she wanted to remain in the custody of her father. Erskine said in other states, children can have a say but they will also have an independent voice to speak and advocate for kids in those situations.

Erskine said the child legal advocacy system has been defective for quite some time. "It's a parent-focused agency to the exclusion of a child's best interest, so my prediction is there will be more child fatalities."

Watch: Adopted fathers of Harmony Montgomery’s brother fight for change in custody system that failed her