Police said the child was in his car seat all alone with his window cracked, but the air conditioning was not on. He was seen crying and sweating profusely, with his nose dripping.
With no time to spare, Edaya Allison recorded the rescue on her cellphone.
The woman seen in the video opening the car door is her sister, Lilach Butler. Butler said another shopper initially waved the sisters down after noticing the toddler in the hot car.
"Everything happened for a reason because if I wasn’t standing at that door, she wouldn’t have called me," Butler said.
In the video, the women say it was more than 80 degrees outside at the time.
>> Read more trending news
Less than a minute later, Butler got the door open. The sisters own a local locksmith business.
"The baby held on to me as if I was his mother," Allison said.
Allison said she called 911 and the mother came out about 10 minutes later.
The Target on Cobb Parkway is in Marietta’s jurisdiction and despite leaving the child in the hot car, police did not charge the mother.
A spokesman said the case is still open and investigators are reviewing the facts to make sure the safety of the child is protected.
"I was shaking. I was in tears because I just couldn’t believe some woman would let this happen to their child," Allison said.
Paramedics checked on the boy and gave him water. He's doing OK.
The rescuers believe he was by himself for at least 15 minutes.