Leaving children unattended in a vehicle with the ignition key (smart key) is dangerous even if the key is not in the ignition switch or ENGINE START/STOP button is ACC or ON position.

Children copy adults and they could place the key in the ignition switch or press the ENGINE START/STOP button. The ignition key (smart key) would enable children to operate power windows or other controls, or even make the vehicle move, which could result in serious bodily injury or even death. Never leave the keys in your vehicle with unsupervised children, when the engine is running.