@maxdancona,
You are not much of a Physicist or a decent teacher. Sorry.
Einsteins words should be almost sacred to you as a believer.
"If you cant EXPLAIN it to a child, they you don't understand it yourself"
Are you here admitting that you don't really understand it yourself? and that's why you can not explain to to a child?
I believe that a number of other prominent Physicists also repeated that very phrase, such as Richard Feynman.
You example of the Earth moving and the car stationary is INVALID.
You have chosen o IGNORE the CRITICAL information that I gave to you, the fact that there is a whole Planet crawling with cars, people, horses, all going in every conceivable direction at the same time.
This precludes absolutely any explanation other than the Earth for everything on it, is effectively absolutely stationary, and its the people, horses and cars that are doing to moving. Even an observer in a passing spaceship would conclude the same.
You get to use whatever object is suitable for the task at hand, and can truly say its stationary, FOR ITS IMMEDIATE LOCALITY, pertinent to the situation.
For Earthlings, the Earth is totally stationary, and that is perfectly correct.
For someone on the other side of this universe, who want's to destroy the Earth with a cosmic ray gun, the Earth is anything but "stationary".
"Absolute stationary" is real but its relative to the set of objects that are inter related. The Earth and its mobile inhabitants, the Sun in this solar system, the Center of the Milky way relative to this solar system, these are all correct examples of truly stationary references, because Physics of motion is only valid for the interrelated objects as a set.
My cars engine has a piston which is moving in a totally stationary engine block, irrespective of the motion of the car on the road.
The engine block is moving with the car which will become really apparent when the car meets the stationary Tree.
See, I can easily explain to a child my understanding of Physics, and the child or reasonable adult gets it straight away.
Now lets hear your story.