The spot with the “maximum kinetic energy” should be on the lowest point of the roller coaster, at the far left side on the bottom.

At this point, the roller coaster car will have the highest speed and therefore the highest kinetic energy, as it has converted most of its potential energy into kinetic energy due to gravity pulling the car downward. This point will likely be where the car reaches its maximum velocity and experiences the greatest force of acceleration.

make it sound like a 5th grader

The spot with the most zoom-zoom energy should be at the very bottom of the roller coaster, on the left side. That's where the car will be going super duper fast because of gravity pulling it down. It's like when you slide down a slide really fast - wheeeeeee!