I auditioned for The Secret Garden using a little-known piece from A Tree Grows In Brooklyn.
"If You Haven't God a Sweetheart" is chorus number in the show, but the kids sing a section of it too, so it's pretty age appropriate. It's got a very sweet, earnest melody. It's great for showing off a pure, young sound.
I got the role despite being on the old side (fifteen, but I was about 4'11) so I guess it worked pretty well.