여러 자녀 중 첫 번째로 태어난
being the first child born to a particular person or couple; eldest among siblings
예문:
"She felt a deep sense of responsibility as the firstborn daughter in the family."
"The firstborn son was expected to take over the family business eventually."
부모에게서 태어난 첫 번째 아이
the first child born to a parent or parents
예문:
"Their firstborn is already starting kindergarten this coming September."
"Historical inheritance laws often granted the entire estate to the firstborn."