Harper, 25, faces two counts of felony murder and two counts of aggravated child neglect in the Aug. 2 deaths of her 2-year-old daughter Savannah Marise and 3-year-old son Daniel Marise outside her Smyrna, Tenn., home, Gannett Tennessee reported Tuesday.
Smyrna police said Harper placed the children in the car in her driveway before going into her home and falling asleep, awaking three hours later to find them dead.
Her court-appointed attorney, Gerald Melton, referred to the incident as a "tragic accident" at her first court appearance.
Harper's arraignment in Rutherford County General Sessions Court is scheduled for Tuesday.
Notable deaths of 2014 [PHOTOS]