Actually, that's incorrect. There's a strong social prestige incentive for your one child to be a boy rather than a girl.
There's a strong economic incentive for you to have a girl: there's a tradition of reversed dowries in China, and girls are rare, so the benefits are high.
Perhaps that was the historical reason boys are high prestige, but modern China has huge opportunities for women (who "Hold up half the sky", as Mao put it).
China was a society of prima genitor, like Europe; boys are high prestige because they carry on your family name. All praise to the eldest son!
