My kids are almost 6 and 2 and I would never ever leave them in the car like that, going inside a building where they are out of view. And, yes, why wasn't the 2 year old restrained in a car seat? Being the neglectful kind of person that would leave his kids alone like that, makes me wonder if there even was an appropriate seat for the toddler. And, I agree, what happened with the 4 year old? So so scary!
My big question is why the heck did he leave the keys in the ignition?? If I ever walk away from my kids in the car, like at the gas station when I step inside to pay, I always lock the doors and take my keys with me, even though they are both safely in car seats and I am all of 10-20 feet away. It really makes no sense that he wouldn't at least lock the doors and take the keys.
Makes me wonder if he was drunk or high, there are so many levels of neglect and not thinking straight.