Randall Lee Vaughn, 41, and Mary Lavonne Vaughn, 58, of Surgoinsville, have both been indicted for first-degree murder, two counts of aggravated child neglect and child abuse, the Kingsport (Tenn.) Times-News reported Thursday.
The couple forced Alexa Linboom to drink more than four 12-ounce bottles of grape soda and an unknown amount of water as punishment for taking some of her stepmother's grape soda, said Attorney General Berkeley Bell.
"That led to her brain swelling and all of her systems shutting down, and to her eventual brain death," the official said.
The couple also failed to care for the child after she became ill, Bell said. "Our position is it was a matter of several hours after the child started exhibiting serious symptoms, after the child was screaming out in pain, went into a paralyzed state, and became unconscious."
The parents took Alexa to a Hawkins County hospital emergency room on Jan. 1, 2012, where she was airlifted to a children's hospital in Johnson City. She died two days later.
A two-year-long investigation determined the child died of acute fluid/water intoxication causing hyponatremic encephalopathy, a condition in which sodium levels drop below normal levels, causing water to enter the brain and produce swelling.
The death was ruled a homicide.
Five other children also lived in the home at the time of the incident, police said. They have been placed in foster care.
Bell said the Vaughns had no previous history of child abuse, but that they used "some alternative forms of punishment."
The couple remained in jail on $500,000 bond each.