Jasmine Green is thought to have fallen asleep between the seats on the ride back from a field trip to Chuck E. Cheese in Jonesboro, Georgia.
When the children arrived back at the center, staff failed to notice she was still in the vehicle - and didn't realise she was missing for more than two hours, as temperatures soared into the 90s.
Her death came just one day after a nine-month-old boy in South Carolina was found dead when his father left him inside his car for four hours.
It also emerged Marlo's Magnificent Early Learning Center had been cited by the state before for not properly documenting a field trip, and was supposed to have introduced a proper system by the end of March.
Jasmine's distraught parents sobbed outside as they questioned how staff could have left her in the vehicle, where temperatures inside are likely to have reached up to 138F after 15 minutes.
April McAlister said: 'They left my baby in the van... forgetting that she was in there. I want to see justice served.' Read More