They were last seen about 4 p.m. Sunday afternoon in Waitsburg.
Authorities say the children, a 2-year-old boy and a 4-year-old girl, may be in danger because of mental-health issues involving the father, John Baugher.
The car the three were believed to be in is described as a 1978 brown Volkswagen van with Washington license plate 349 NRK. However, the vehicle was found unoccupied in Stevens County earlier Monday morning. County deputies are checking the surrounding areas for the children and their father.
Four-year-old Remi Baugher has blonde hair with hazel eyes and stands at 3 feet, 1 inch tall. She was last seen wearing a pink jacket with a heavier yellow jacket over the top, blue jeans, and Strawberry Shortcake shoes.
2-year-old Lars Baugher also has blonde hair with green eyes and is 2 feet, 7 inches tall. He was last seen wearing a brown or green jacket, blue jeans, and black Converse shoes.
The father, John Baugher, 34, has brown hair with green eyes. He is 5 feet, 7 inches tall and weighs 140 pounds.
Anyone with any information on the whereabouts of the children should contact Walla Walla County police at (509) 527-1960.