Dual-core family refers¹ to a family where both husband and wife are the only child or the single “core” of their own families before they got married². The new family, of course, has two “cores” as neither of the couple knows how to behave not as a “core” in a family.

“双核家庭”指夫妻双方均为独生子女的家庭，双方在婚前都是各自家庭中的“核心”，因此称为“双核家庭”。在两人建立的新家庭中，双方都不知道该如何以“非核心”的方式行为处事，于是，家里就出现了两个“核心”。

For example:

The number of dual-core families has been growing in recent years since more and more post-80s are getting married.

随着越来越多的80后走入婚姻殿堂，双核家庭的数量在近几年不断攀升。