Siblings Hannah Anderson, 16, and Ethan Anderson, 8, were abducted from Boulevard, Calif., on August 3, 2013 around 5 p.m.
The suspect in the abduction is 40-year-old James Lee Dimaggio, who was last seen driving a blue Nissan Versa four-door with the Calif. license plate 6WCU986.
An Amber Alert was issued statewide in California, but the suspect may be driving through Texas or Canada and could drive through Washington.
The Amber Alert was in effect early Tuesday for the two missing children of a woman whose body was found inside a burned rural house near the U.S.-Mexico border, and authorities said the man suspected of killing the woman may have abducted the kids.
Authorities were trying to locate Hannah and Ethan whose mother, Christina Anderson, 44, was one of two people found dead by authorities sent to extinguish the fire Sunday night, a San Diego County sheriff's statement said.
Hannah is approximately 5-feet, 7-inches tall and weighs 115 pounds. She is white with blonde hair and blue. Hannah also has pierced ears and a nose stud.
Ethan is white with sandy blonde hair. He is 4'11" and weighs 65 pounds.
Dimaggio is described as 5 feet, nine inches tall with brown hair and brown eyes. He weighs 150 pounds.
The suspect owned the home in Boulevard, some 60 miles southeast of San Diego, and lived there alone, the sheriff's statement said.
DiMaggio was in a "close platonic relationship" with Anderson, the sheriff's statement said without further explanation.
Anyone with information is asked to call the San Diego Sheriff's Department at (858) 565-5200.
A second body, that of a child, was found dead in the rubble of the house's detached garage, but the identity and manner of death remained undetermined. Authorities who released the news of the deaths Monday night wouldn't say whether the body may have belonged to one of Anderson's children.
A dog was also found dead inside the house.