Police say Cassandra Robertson has been missing since Monday.
The suspect believed to be involved is Nickie Robertson, 39.
Cassandra is described as a white female, age 4, approximately 2 feet 6 inches tall with brown hair and blue eyes. She was last seen wearing a gray zippered shirt with a Hello Kitty logo.
She has an eye infection requiring medicine. Her mother, Nickie, has a history of suicidal tendencies and substance abuse.
Nickie is described as a white female, 5 feet 6 inches tall, 145 pounds with brown hair and green eyes. She was last wearing blue jeans and a black shirt.
The suspect vehicle is a silver, 2006 Nissan Quest with Missouri tags: FG2-D5J.
Robertson may be headed for Las Cruces, N.M., or Colorado.
Anyone with information should dial 911 immediately.