their 'firstborn' [='eldest, oldest'] child
Parents often spoil their 'firstborns'.
(..) and healthy. My congratulations, Lord Bolton. Congratulations, Father. I look forward to meeting my new brother. You'll always be my firstborn. Thank you for saying that. It means a great deal to me. - - ( groans ) Maester Wolkan, (..)2016 TvShow: Game of Thrones Title: Home Season: 6 Episode 2