The kids’ mother, Lori Vallow, was arrested in Hawaii on Thursday.

Home surveillance footage shows missing 7-year-old Joshua “JJ” Vallow days before he and his 17-year-old sister, Tylee Ryan, disappeared.

The video, obtained by East Idaho News, shows JJ playing in the front yard of his home with friends and was shot on Sept. 17, nine days after he and Tylee were seen at Yellowstone National Park on Sept. 8 with their mother, Lori Daybell.

The footage is the last image of JJ before his disappearance and is being used by police to piece together a timeline of the children’s last known whereabouts.

JJ, who has autism and was adopted by Vallow, was last seen alive on Sept. 23 at Kennedy Elementary School in Rexburg, Idaho, according to a probable cause affidavit for Lori Vallow’s arrest obtained by ABC News. The next day, Vallow called the school and informed them that JJ would no longer be attending and that she would homeschool him going forward, but requests for JJ’s transcripts were never made.

No witnesses have seen JJ since Sept. 24, police said. Tylee has also been missing since September.

The children’s safety came into question in November after Kay Woodcock, the biological grandmother of JJ, called Rexburg police and requested a welfare check, the affidavit states.

When police arrived at Vallow’s home on Nov. 26, they were met by Vallow’s brother, Alex Cox, and her fourth husband Chad Daybell, whom she had married about four weeks earlier. When police found Vallow later that day, she claimed JJ was staying with a friend in Gilbert, Arizona.

That friend later told investigators that Vallow and Daybell had contacted her separately with requests to falsely tell police JJ was with her, according to the affidavit.

Vallow and Daybell were gone when police returned to the home the next day.

Vallow was arrested on Thursday in Hawaii, where she and Daybell have been living, on charges of felony desertion and nonsupport on dependent children, weeks after she failed to comply with a court order to produce them in Madison County, Idaho, on Jan. 30.

Her bail was set at $5 million. She is scheduled to appear in court on March 2, when she is expected to be turned over to Idaho authorities.

ABC News’ Ella Torres contributed to this report.