There had been much debate among the colonists regarding when children should be allowed on the surface. Ultimately, for reasons unimportant to this story, they had settled on the age of four, in Martian-years, as the appropriate time to introduce children to the world outside. And so, Cas and the other third graders had become the first human children to walk on the surface of another planet.
Air: Generation Mars, Book One
Coming in October
(image: from Scratching the Surface, Luis Peres)