Their first child was conceived on their wedding night.

他们的第一个小孩是在新婚之夜怀上的。

《牛津词典》

She married at 17 and gave birth to her first child shortly thereafter.

她17岁结婚，之后不久便生了第一个孩子。

《牛津词典》

His wife gave birth to their first child, and he was ecstatic about it.

他的妻子生下了他们的第一个孩子，他对此欣喜若狂。

《柯林斯英汉双解大词典》

Helen was their first child. Until she was a year-and-one-half old, Helen Keller was just like any other child.

VOA: special.2009.11.08

Malaria,diarrhea,and typhoid- water-related diseases that are not fatal in First World countries- cause half of the child deaths in Yemen.

VOA: standard.2010.04.01

As the first-born child (and an undeniable Type Double-A personality), I started taking over big things for my mother when my father was still in the nursing home.

FORBES: How To Be A Loving Advocate For Your Parents

This comes just two years after the tabloid-staple couple peddled pictures of their pouty newborn--and first biological child--Shiloh Nouvel.

FORBES: Magazine Article

Primogeniture refers to the right of the first-born child to inherit the entire estate.

CNN: I like one child more than the other