A child born to a person is commonly referred to as their "offspring" or "child." In more specific terms, they may be called a "son" if male or a "daughter" if female. The term "descendant" can also be used to describe a child in relation to their parents in genealogical contexts.
You call a person born in Ireland, Irish.
You would call this person a child. By the time a child reaches puberty, he or she knows.
You can call your child whatever you want I mean it's yours.
A firstborn child is the first one born to a couple or individual; normally the eldest child.
Mature
Human
A person under a legal guardianship is called a Ward.
A parent/guardian
German
pedomihner
An Anglesubriacht
Scottish :)