Brin David. Glory Season

Twenty-six months before her second birthday, Maia learned the true difference between winter and summer.
It wasn't simply the weather, or the way hot-season lightning storms used to crackle amid tall ships anchored in the harbor. Nor even the eye-tingling stab of Wengel — so distinct from other stars.
The real difference was much more personal.
"I can't play with you no more," her half sister, Sylvina, taunted one day." "Cause you had a father."
"Did n-not!" Maia stammered, rocked by the slur, knowing that the word was vaguely nasty. Sylvie's rebuff stung, as if a bitter glacier wind blew through the creche.
"Did so had a father, dirty var!"
"Well...then you're a var, too!"
The other girl laughed harshly. "Ha! I'm pure Lamai, just like my sisters/mothers an' grandmas. But you're a summer kid. That makes you u-neek. Var!"
Dismayed, too choked to speak, Maia could only watch Sylvina toss her tawny locks and flounce away, joining a cluster of children varied in age but interchangeable in appearance. Some unspoken ritual of separation had taken place, dividing the room. In the better half, over near the glowing hearth, each girl was a miniature, perfect rendition of a Lamai mother. The same pale hair and strong jaw. The same trademark stance with chin defiantly upraised.
Here on this side, the two boys were being tutored in their corner as usual, unaware of any changes that would scarcely affect them, anyway. That left eight little girls like Maia, scattered near the icy panes. Some were light or dark, taller or thinner. One had freckles, another, curly hair. What they had in common were their differences.
Maia wondered; was this what it meant to have another? Everyone knew summer kids were rarer than winterlings, a fact that once made her proud, till it dawned on her that being "special" wasn't so lucky, after all.
She dimly recalled summertime's storms, the smell of static electricity and the drumbeat of heavy rain on Port Sanger's corbelled roofs. Whenever the clouds parted, shimmering sky-curtains used to dance like gauzy giants across distant tundra slopes, far beyond the locked city gates. Now, winter constellations replaced summer's gaudy show, glittering over a placid, frost-decked sea. Maia already knew these seasonal changes had to do with movements of Stratos round its sun. But she still hadn't figured out what that had to do with kids being born different, or the same, Wait a minute!
Struck by a thought, Maia hurried to the cupboard where playthings were stacked...