Answer:
Iron on a mammal. Mammal on your feet.
My life can be measured in hours. I serve by being devoured. Thin, I am quick. Fat, I am slow. Wind is my foe.
Fatherless and motherless. Born without sin, roared when it came into the world. And never spoke again.
Flat as a leaf, round as a ring. Has two eyes, can't see a thing.
Used left or right, I get to travel over cobblestone or gravel. Used up, I vie for sweet success, used down, I cause men great duress.
I stay where I am when I go off. What am I?
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?