So I got an idea. How about I setup the power wheels so that I can take control of the throttle via radio control? That way, I can just stop the vehicle from a distance without any scary running and shouting. It also improves the chances of me stopping a collision (I don't have to be right nearby), and would even allow me to give rides to my youngest child (1.5yrs; doesn't have the throttle control figured out yet) without needing to walk hunched over next to the vehicle to control the throttle.
Luckily, I have already setup the power wheels to have throttle controlled by a combination of a potentiometer and custom-programmed microcontroller that instructs an RC car's electronic speed controller (ESC) to provide power to the motors (read all about that here: viewtopic.php?f=26&t=1724). All I had to do was hook up another servo cable to my microcontroller that would allow me to plug into a radio receiver. I plug it into the throttle channel (channel 2) of the radio, and update the program on the microcontroller to read the signal.
The big black box is my custom electronics. The radio receiver is just to the right of the black box.
I programmed it so that the throttle position is determined by the potentiometers (throttle and brake pedal on the vehicle itself) by default. But if a signal is received from the radio receiver that is not a neutral position, then the radio signal determines the throttle position. The radio signal will remain in control of the throttle position until both the radio signal and the potentiometers on the vehicle have both return to neutral. After I remotely hit the brakes, if my kid is still holding the throttle wide open, he won't go anywhere when I release the brakes until he first releases then reapplies the throttle.