only child(男女都可以)複數：only children
the only child in one's family 都有 獨生子女 的意思。不過多用only child.
singleton 也可以，不過就是獨生子的意思。
例：過分溺愛獨生子女的父母
parents who dote on their only child.
獨生子女有時被寵壞了。
only children are sometimes spoilt.
而extra births就是“超生人口”，也就是我們平時說的“計畫外生育”，也可以稱為extra children /additional births。根據family planning policy(計畫生育政策)，一般情況下每個家庭只允許生育一個孩子，也就是我們所說的only/single child(獨生子女)。
不過要介紹的是下面這個表示方法：china one.
the term “china one”refers to the child who was born after the 1980s, when china launched the one-child policy. not only are they the family’s only child, but they are also the family’s center of attention. their parents and grandparents would spare no efforts in taking care of them, and would give them anything and everything, as if they were the “emperor” of the family.
china one指的是20世紀80年代中國實行計畫生育政策以後出生的獨生子女。他們是家中唯一的孩子，也是家庭的中心。他們的父母和祖父母都會不遺餘力地照顧他們，滿足他們的一切需要，就好像他們是家裡的“皇帝”一樣。
as a result, most children of the “china one”generation lack independence as they have become so reliant on their families for support. some parents even hired a maid for their children when they go to college. other unfavorable characteristics include: bad communication skills, rudeness, ungratefulness and self-centeredness.
由此，大多數獨生子女自理能力都很差，他們太過依賴家人，甚至上大學以後還有父母為他們雇保姆。其它不太讓人喜歡的特點還有：溝通能力差、不懂禮貌和感恩、以自我為中心等。