New photos show missing Idaho kids in Yellowstone before disappearance

The FBI is asking anyone who visited Yellowstone National Park on Sept. 8, 2019, to come forward with photos, as the agency assists in the case of two Idaho children's months-long disappearance.

The park, located mostly in Wyoming, is the last place 17-year-old Tylee Ryan was seen, according to authorities. Her 7-year-old brother, Joshua "JJ" Vallow, was last seen in Rexburg, Idaho, where the family lived, on Sept. 23, authorities have said.

Photos released Thursday by the FBI show both children in Yellowstone with their mom, Lori Vallow, who was recently extradited from Hawaii to Idaho where she will face numerous charges involving the case.

The photos also show Vallow's brother, Alex Cox, was in attendance for the trip. Cox died about three months later, on Dec. 11, 2019, after he was found unresponsive in his home. Authorities have not yet released information on his cause of death.

The family had traveled to the park in a silver 2017 Ford F-150 pickup with an Arizona license plate CPQUINT, according to the FBI.

The FBI has created a website for the public to upload photos and video at FBI.gov/Rexburg.

The request from the FBI comes a day before Vallow, 46, is expected in a Madison County Court for the first time. She is expected to be read her charges, which include two felony counts of desertion and nonsupport of dependent children.

Vallow and her fifth husband, Chad Daybell, had been living on the island of Kauai in Hawaii since December.

Police have said during the course of their investigation they found "no evidence or verification of anyone providing for the housing, food, clothing, education, or medical care" for the children since September.

The public is asked to continue reporting tips in this case to the Rexburg Police Department at (208) 359-3000 or the National Center for Missing and Exploited Children at 1-800-843-5678 (1-800-THE-LOST).

ABC News' Alex Stone contributed to this report.