Why do they fill childrens jackets with feathers, anyway?

My second son convinced that his little sisters winter jacket is 'full of dead chicks' because it's down feather filled. She was really upset, kind of wearing fur while not knowing.
So she was screaming: "No I'm NOT wearing dead chicks" and came to me to find the truth.

(At least, I seem to be very truthful to her. But she's only four. I know it will change, in about 10 years or so)

I convinced her that her jacket was indeed filled with feathers, but the chicks did not die, they grew new feathers and became healthy, grown-up, adult chickens. My second oldest of nine, standing aside and listening to my reasoning, was in a quite fascist mood.

Didn't stop.

He stated that: "All chickens were killed and slaughtered now, and in the fridge, and one of these days, would end up on her plate."

I sent him to his room.