Answer:
Humans have two that shrink in the light and expand in the dark
Often found in doctor's offices and pirate flags
I start in little but I end in full, you'll find me in half and complete.
I occur twice in eternity. And I'm always within sight.
Blue lives in the blue house, Mr. Pink lives in the pink house, and Mr. Brown lives in the brown house. Who lives in the white house?
Cycle Cycle Cycle.
Easy
Animal
Difficult
Food
Funny
Kids
Logic
What am I?