You said your oldest is 9 years old... I would like to say, at that age, my mother was babysitting the neighbor's kids. She could call my granny if she had any questions or needed help, and my granny could walk over. I was babysitting by the age of 12 or 13. I do not think you did anything wrong, personally. Your daughter had a phone. She knew what to do and what not to do. If it had just been the 2 year old or the baby in the car, that's different, but 9 years old is old enough to know when to get out of the car if it is too hot or they can't breathe for some reason. It is old enough to unbuckle herself and her siblings, and then wait for you or go into the store. That is different than leaving a toddler who can't speak for themselves in the car alone.