Missing Idaho kids mystery: Older son begs mom to come home

Joshua Vallow, 7, and Tylee Ryan, 17, have been missing since Sept. 23.

Months into the search for two missing children -- and the hunt for their mother, Lori Vallow, who police said fled town -- Vallow's older son is begging her to come home.

"Mom, I want to talk to you like I'm sitting across the room from you," Colby Rayn said in an emotional video posted to YouTube.

"I just need this to end for Tylee and JJ," he pleaded. "I need this to end for you. I need this to end for all of us."

His siblings, Joshua Vallow, 7, and Tylee Ryan, 17, have been missing from Rexburg, Idaho, since Sept. 23.

His mother, Lori Vallow, who is Joshua's adopted mother and Tylee's biological mother, knows where the missing kids are or what happened to them but has refused to help with the case, according to Rexburg police.

The children's grandparents held a press conference on Tuesday asking the public for help.

"Can't tell me that someone doesn't know something about these children to give us one piece of information to find them," Larry Woodcock told reporters. "We want information and we want closure."

Police said last week they believe "Joshua's and Tylee's lives are in danger."

Authorities believe the kids' disappearance is linked to the October death of Chad Daybell's former wife, Tamara "Tammy" Daybell.

Her death initially was thought to be natural, but investigators later found it suspicious and her remains were exhumed, police said.

Chad Daybell married Vallow a couple weeks after Tamara Daybell's death.

Fremont County Sheriff Len Humphries said it'll take several more weeks for an autopsy to be completed, due to toxicology tests stemming from the allegations that Tamara Daybell was poisoned.

The safety of Tylee and Joshua was called into question in November, when extended family reported that they hadn't been able to speak with Joshua since September.

When officers in November spoke with Vallow and Daybell, the couple said Joshua was staying with a friend, police said. Officers later learned Joshua wasn't there.

When police went back to Vallow and Daybell with search warrants, they found the couple had "abruptly" left Rexburg.

"We pray that they are all together, but we don't know that as a fact," said Kay Woodcock.

On Friday, authorities served a search warrant at Chad Daybell's Fremont County, Idaho, home, seizing computers, phones and documents, according to ABC Idaho Falls affiliate KIFI.

Chad Daybell's sons still live at the home, KIFI said.

Police also allege that Vallow and Chad Daybell lied about Vallow's children weeks after Tammy Daybell's death.

They allegedly told people "that Lori's daughter had died a year before the death of her father, which is untrue," police said. "Around that same time Chad told another witness that Lori had no minor children."

Humphries said they don't have enough evidence right now to issue an arrest warrant for Daybell and Vallow, that "they're not suspects at this time."

Sean Bartholick, an attorney for Vallow and Daybell, said in a statement last month that she's a "devoted mother" and he's a "loving husband."

"We look forward to addressing the allegations once they have moved beyond speculation and rumor," Bartholick said.

Bartholick did not immediately respond to ABC News' request for comment on Tuesday.