Answer:
Tickle with your fingers and a song it will sing. Be careful, though, you may break a string. What is it?
I am the yellow hem of the sea's blue skirt.
They are the group who manages the winged engines of war.
What is yours but only used by others?
This is the main ingredient in spaghetti and Mac-N-Cheese.
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.