Training supermarket van drivers, there are large blind spots all around. I've seen bicycles abandoned in front, invisible to the driver, and one time, a child crouched in front, hiding from a friend. We always recommend, that if moving away forward, walk around the front of the vehicle before getting in, or if reversing, walk around the rear. The time it takes to get in, and get ready to go, the situation can change, so whenever possible, manoeuvre on arrival, not on departure, so you can drive away. Sometimes, a reverse is necessary, so walking around the back ensures the area is clear, but it may not stay clear.
And people, even adults cannot be trusted. A while ago, turning at the end of a cul-de-sac, with a supermarket van, the driver turned to the right, and while selecting reverse, checked his left mirror, then his right, then the left again. Seemed all clear and was about to move backwards. I stopped him. As he looked right, I looked left, having some view in the left mirror from the passenger seat. As teh driver moved his eyes from left mirror to the right, a woman, phone in left hand, pushchair in right, walked across behind. Driver not seen her. She then stopped, behind the van, to finish her text message. Van had no camera, but had the reversing beeper squeaking, and of course the diesel engine running, and the fridge above the cab running. She took a few moments to appear to our right. Without a passenger noticing, driver would have reversed into her and the pushchair. Driver did all he could, pedestrian was a 'phone zombie'.
I hold my little ones hand where ever we go. I cannot understand how someone can let a toddler loose in a busy carpark.
Sadly you seem to be in the minority, most parent seem to prefer holding a phone, instead of their child.
So many times in car parks, parents arrive back at the car, let go of toddler, tell it to stand still, while they load the shopping into the boot. As if any toddler would stand still! Then they yell at the toddler if it's moved. Surely, leave the shopping, install the toddler into its seat, shut the door, with child locks activated, then load shopping knowing all is secure. Seems difficult. Is the fear of someone stealing the shopping greater than that of losing the child?