Investigators say the little girl and her family had come home from a shopping trip around 2:00 p.m.
The parents had assumed the toddler went up to her grandparents, who lived on the floor above. When she did not turn up there, the family began searching for her.
She was found inside the van around 5:00 p.m., strapped into her child safety seat.
Efforts to save the little girl were unsuccessful.
She was pronounced dead at the scene.
Atlantic City Police are investigating.
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