Riddles

Out of the eater, something to eat.
Out of the strong, something sweet.

Round as a marble, blue as the sea,
Unless I am green, or brown, maybe!
Smile, and I shine my window pane
Frown at me and down comes my rain
I see all things but nothing I hear
Sing me to sleep and I disappear.

Deep within me is a bird,
and in that bird another me,
and in that me a bird again,
Now what am I, in letters three?

Have Fun!