The other victims were aged three, five and seven.
The fire broke out late on Tuesday night on the second floor of a duplex in Conyers.
Police Major Mike Waters told Atlanta television station WAGA-TV that the children's mother rushed upstairs but was only able to save her 5-year-old son by throwing him out of a window.
The boy suffered a broken collar bone and was transported to a local hospital.
The mother who suffered 40% burns, also jumped out of the window.
A grandmother managed to get out of the building unharmed.
Major Waters told reporters that a neighbour tried to help.
"There was one neighbour that tried his best to get in a rear window but the flames were too strong, and there was no way he could get in," he said.
Police officers arrived on the scene quickly after the fire was reported.
Flames were already coming down the stairs, as they tried unsuccessfully to put it out with handheld fire extinguishers.
The cause of the fire is being investigated.