When my oldest was 4 she was left in the car. It was me, my sister, my niece, and my daughter. I had my hands full so I assumed that my sister would get my child and hers out of the car. When my sister came inside without my daughter I realized she was still in the car. I went out to get her and found her on the floor crying. She was so upset that she had been forgotten, she never even realized that she was big enough to open the door and get out. I don't know if this is what happened here but mine would not have gotten out of the car on her own.