Round as Houses: Sci-fi/Fantasy

Inseparable they were when they were little, cute as buttons, round as houses, and green as the sky. As they grew older, their skin paled to yellow, they lengthened out a little and grew proper legs, they lost their cuteness in adolescent awkwardness, but they stayed inseparable. The mothers tut-tutted over it, of course: children of different castes weren't supposed to want to play together at all, much less in preference to children of their own society. At first, they let it slide because the children were too young to know better. Later, they let it slide because it had become plain that Lila would grow up to be a potential Queen, and nobody wanted to irritate one who might someday rule them all.

Inspiration: 'inseparable'
Story Potential: High.
Notes: If only because I love-love-love that opening line. And the society set-up is neat. Could be either science fiction or fantasy or--no, really, I guess it would have to be one or the other/both.