Firstborn
Eldest child
A firstborn (also known as an eldest child or sometimes firstling) is the first child born to in the birth order of a couple through childbirth. Historically, the role of the firstborn child has been socially significant, particularly for a firstborn son in patriarchal societies. In law, many systems have incorporated the concept of primogeniture, wherein the firstborn child inherits their parent's property.
From Wikipedia, under CC BY-SA. More on occurri.