Answer:
I know a word of letters three. Add two, and fewer there will be!
A time when they're green. A time when they're brown. But both of these times, cause me to frown. But just in between, for a very short while. They're perfect and yellow. And cause me to smile.
I do not breathe, but I run and jump. I do not eat, but I swim and stretch. I do not drink, but I sleep and stand. I do not think, but I grow and play. I do not see, but you see me everyday.
I grow where no flower grows, where no light touches the walls, up or down, that I don't care, was here before people were.
You’ll have me at night and if you remove the first letter I denote the top, such as on a train
When is it bad luck to see a black cat?
Difficult
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?