Son makes heartbreaking plea to missing Idaho mother Lori Vallow to reveal missing children's whereabouts

The oldest son of missing Idaho woman Lori Vallow has begged his mother to reveal the location of his two younger siblings, who have been missing since September.

"I want to talk to you like I'm sitting across the room from you," the 23-year-old Ryan said in YouTube video message titled "Mom." that was posted Sunday. "You have the power to end this. ... I want you to end this. I want you to end it, for everybody. For the kids, for yourself, for all of us. This can end."

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Joshua Vallow, 7, and Tylee Ryan, 17, are the focus of a nationwide manhunt by the FBI after police in Idaho police requested assistance with the case. Authorities believe Lori Vallow, 46, knows the location of her children but refuses to cooperate with investigators. They also believe the children's lives are in danger.

In a bizarre twist to the case, Vallow's first husband, Charles, was fatally shot in July during a confrontation with her brother Alex Cox, who claimed self-defense and was never arrested. She then married Chad Daybell, 51, whose first wife, Tammy, died of natural causes in October.

On Dec. 20, investigators said the children's disappearance could be related to Tammy's death, and her body was later exhumed to determine if there is any connection to the current investigation.

Vallow and Daybell have left Idaho and are currently on the run.

"I'm so upset, I can't even tell you. I can't even tell you how much my feelings hurt," Ryan said in the video. "I don't have words to formulate for you. I don't. I have so much anger. ... I have so many things that I want to ask you. I have so many things that I just want to put into place and I have a million other people who want the same thing and it just sucks."

Ryan said he's struggled with the emotional pain from his siblings' disappearance and is deeply concerned for his family's safety. He also asked his mother to put the children on Facetime to prove to the police that they are still alive and safe.

"I want you guys to be safe and I want you guys to be okay. But we're way past the point of that," he added. "I can't call my own mom, I can't go see my siblings. Everything that's happened, everything that's been going on, I can't even tell you. I've never felt this way. I"ve never had my heart broken like that."

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Brandon Boudreaux, a relative, told Fox 13 Salt Lake City that Vallow joined a doomsday “cult” with Daybell, but authorities have yet to say if there is any religious connection with the case.

Fox News' Robert Gearty and Louis Casiano contributed to this report