Jaxon Taylor was being babysat by his grandparents while his mother, who works night shifts, caught up on her sleep at home.
According to CNN, Kyle and Meta Hendershot decided to take the 11-month-old baby to church in Chickamauga, along with one of their adult daughters and another grandchild.
When they arrived home, they went back inside the house.
It was around two hours later, when the boy's mother awoke and asked where her son was, "that the grandparents realized that the child wasn't (inside).”
Walker County Sheriff Steve Wilson told CNN that the baby boy’s mother, a nurse, rushed outside to have her worst fears realised; Jaxon was still in the car - and the temperature in Georgia, USA, has, by that point, hit 90 degrees.
He added: “[The] temperature in a closed vehicle can reach as high as 131 to 172 degrees in as little as 15 minutes.”
The mother desperately attempted CPR on the little boy, but he was pronounced dead at hospital.
Explaining how the terrible situation came about, Wilson said: "There was a lack of communication within the three adults.
“They assumed that one of the others had brought in the child and laid him down. They didn't communicate who would get the child."
An autopsy has yet to be completed, but it is expected to reveal that Jaxon died of heatstroke.
No charges have been filed, but the death - thought to be ‘accidental’ - is being investigated by the Walker County Sheriff's Office.
The family have, so far, raised more than $2000 on a GoFundMe page designed to help with the costs of relatives coming to comfort the boy’s mother.
“My fiancées family has traveled from out of town to support and comfort us, to force us to eat, drink and move when we would lay in bed and cry,” his mother said.
She added that Jaxon will “forever be in the deepest crevices of my heart.”
An average of 38 children die trapped in hot cars each year, according to KidsandCars.org.