We are little airy creatures
All of different voice and features
One of us in "glass" is set
One of us you'll find in "jet"
T'other you may see in "tin"
And the fourth a "box" within
If the fifth you should pursue
It can never fly from "you"
What are the five "little airy creatures"?
This is a clever riddle, but the quote marks immediately told me that it was about letters found in certain words. I suggest you take the quote marks out -- it will still be clued fairly. Even with that change, the line "One of us you'll find in jet" is still too much of a hint because "in jet" will be taken to mean "in the word 'jet.'"