Do people actually open their drivers front doors and let their children climb into the DRIVERS seat and then walk away for any reason? I doubt it is supposed to allow them to drive... but in what circumstance does someone ever do this?
Why would a child that small ever be allowed to climb into the drivers seat without the parent / caretaker either already in the car, or getting in right after them. A child like that should be either getting in, or placed into a child seat, and they should never be in the drivers seat, let alone "when someone then walks around the front of the car after they do so".
When I was a kid it was common to use a parked car for
* easter egg hunt hiding places
* hide and seek
* make believe
* place to get out of the sun
and so on, it was just another location available to us and was safe as could be. No way in the world you could even turn the steering wheel let alone take the car out of Parking gear.
With phone as key and no start button a car is no longer safe for play. An adult coming to get a kid out of the car because it's time for lunch or whatever would turn the car on and enable the OPs scenario.