What do the children do when the sun comes out?

When the sun comes out the children run among the trees, lay out, laughing, push each other, play hide-and-seek, tag, and squinted at the sun till tears ran down their faces.

The children were jealous of her and her possible future (going back to Earth). They hated her pale snow face, her waiting silence, and her thinness.

Why do the children do that to Margot?