Solomon and Marozhina Sukonick, were last seen at 8 p.m. Thursday near the 1000 block of West Avenue J-8 where their father, David Sukonick, picked them up, the department's Lancaster Station said.
The 9-year-old girl, Marozhina, is described as 4 feet 4 inches and 90 pounds with brown hair and brown eyes. She was last seen wearing pink shorts and a white shirt.
Solomon, the 9-year-old boy, is also 4 feet 4 inches and 90 pounds with brown hair and brown eyes. He was last seen wearing blue shorts and unknown colored shirt.
The 71-year-old father, David Sukonick, is 5 feet 7 inches, weighs 135 pounds and has brown hair and green eyes.
David Sukonick was last seen driving with the children in a 2011 Black Lincoln Town Car with California license plate #SOLOYST.
Sheriff's officials said there is concern for the children's well-being.
Anyone with information was encouraged to contact the LASD Lancaster Station at (661) 940-3855. Those wishing to remain anonymous may call Crime Stoppers at (800) 222-8477 or visit lacrimestoppers.org.