The mother of two children missing since September has violated a court-ordered deadline to bring the children to Idaho authorities Thursday, paving the way for her to possibly be extradited to Idaho from Hawaii to face charges.

Police said Lori Vallow and her new husband, Chad Daybell, lied about the children's whereabouts and even their existence. Seven-year-old Joshua “JJ” Vallow and 17-year-old Tylee Ryan haven't been seen since late September, said police in Rexburg, Idaho.

Authorities have said they believe both their lives are in danger.

“The only word coming to mind right now is ‘monster,’” Kay Woodcock, JJ's grandmother, said during a press conference Thursday evening. “All this has just been very disheartening. ... I'm a lot less optimistic at the moment.”

This combination photo of undated file photos released by National Center for Missing & Exploited Children show missing children Joshua "JJ" Vallow, 7, left, and Tylee Ryan, 17. (National Center for Missing & Exploited Children via AP)

Vallow married Daybell, the author of several religious-themed fiction books about prophecies and the end of the world, in October 2019 — a month after her children were last seen alive and just days after Daybell’s 49-year-old wife, Tammy Daybell, died Oct. 19 in her Idaho home. Her death was initially ruled due to natural causes. Authorities later exhumed her body for an autopsy but the results have not been released, AZ Family reported.

Police questioned Daybell and Vallow about the missing kids in late November, and the couple left town before police returned the next day. On Saturday, they were stopped by investigators in Hawaii, served with the order to produce the kids, and then searched.

A contempt of court charge is generally a misdemeanor under Idaho law, with a penalty of just five days in jail and a $5,000 fine. But Kay Woodcock said authorities told her it could be used to seek Lori Vallow's extradition.

“We now know that there's some recourse that can happen after this,” she said. “They're going to make her accountable to law enforcement.”

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Family members of Lori Vallow have accused her of joining a cult. Before moving to Idaho, Lori lived in Chandler, Ariz., with her two children.

Fox News' Danielle Wallace and The Associated Press contributed to this report.