37-year-old Julia Gorman and her live-in boyfriend, 30-year-old Robert Andrew Palmer, were booked into J. Reuben Long Detention Center Friday afternoon.
Gorman is charged with homicide by child abuse. If convicted, she could be sentenced to 20 years to life in prison.
Palmer is charged with unlawful neglect of a child, after police say he knew about the abuse, but failed to report it.
Police say the abuse happened at the couple's home, on Highway 129 in Galivants Ferry, on Friday, July 11th, but the couple did not take the child to the hospital until Monday, July 14th.
Police say the boy's father called them on July 14th, possibly from Virginia, and said his child had been hurt, and was en route to Conway Medical Center.
Police arrived at the hospital and interviewed witnesses.
The child was flown to Medical University of South Carolina in Charleston that night, but died Wednesday, July 16th.
An autopsy will be performed Saturday to confirm the cause of death, but Horry County Coroner Robert Edge says it appears the toddler died from a head injury.
Friday night, NewsChannel 15 stopped by the neighborhood where the couple lives. Neighbors and the couple's landlord said they had interacted with Gorman, Palmer and the boy several times and never noticed anything out of the ordinary.
Police were not able to confirm where the boy's mother lives but the landlord said she lives in Arizona, and had come to see her son two months ago.