A boy was found abandoned near the Atlanta City Detention Center on Peachtree Street Monday, police said.
Ethan Parker's mother is believed to be Lakeish Parker Robinson, Atlanta police spokesman Lukasz Sajdak said.
Police say the 4-year-old's older sister told them that she dropped the boy and their mother off at the Decatur train station Monday.
A Good Samaritan later found him alone on the steps of the jail, took him inside and called 911.
Family members say the boy's mother has an addiction problem. Police believe she may have taken advantage of the "safe haven law." Officers are still working to locate her.
The boy was taken to a local hospital, where family members picked him up.