It could also be used as a punishment! Maybe the first or secondborn did something to earn their parents' ire and in order win it back they need to go adventuring.
(After writing that I realize I did just describe Zuko but my thought process was more along the lines of... the parents are actually giving their kid something achievable lol.)
Or it could be a literal quest. Elderly father with a physically fit kid, or perhaps a magic-studying freak kid, "Go, my son, retrieve your grandmother's enchanted necklace from the lich king." If the DM has a problem with wealth - Kid gets robbed two days into his quest, party NEEDS to buy something expensive, the people in the upcoming village only trade in seaglass, etc.
Like literally there's so many ways to approach this sort of thing and tbh more players and DMs alike need to like... be creative and NOT say "you can't have this benign and possibly inconsequential character trait because it doesnt make sense or its impractical."
Like... yes you can! A lot of DMs say no to letting their players have evil characters because it disrupts party goals but like... I've played lawful evil characters and they don't disrupt the party. Their goals have just also Aligned with what the party wants/they need the party to function in order to get what they want.
I'm also playing a monstrosity in my next campaign. I went online to see what most people had to say about playing literal beasts and most of it amounted to "You CANNOT play an animal because you need to TALK to your party members and its such a huge problem to not talk!" So many people were saying this. So. Many.
I thought that was horseshit, but I brought it up with my DM anyway and the convo went as follows:
Him: ":/ As the arbiter of this world I decree that your beast can speak. Problem solved."
Me, intentionally parroting something I saw online: "but HOW can I speak?"
Him: "idk you're creative figure out a fun reason. I GUESS i could come up with something myself but I assume you'd like the freedom to make up your own backstory?"
Me: "Hell yeah!"
idk people always saying "This can't work!" outside of stats and math kinda sounds like a skill issue to me