
A daughter - both of her children are girls. The oldest just dresses more boy-ish
I've heard Korean doesn't have gendered pronouns, which is why you'll often see low-quality translations mix them up, because they just tend to put everything throught MTL and don't even check if things fit the context. The pronoun issue also applies to you/me pronouns, at least I've noticed they tend to get messed up a lot in bad translations, when in the context the opposite would make more sense.
Sometimes messages are still unclear to me, but being aware of this helps make sense of things better ╮( ̄∇ ̄")╭

Or it could be like in the hunterxhunter where the gender is still undecided. Like in one of the character are a girl in the first early episode (he has boobs in the early chaps. Not sure if it is the early version or the latest version though). Now, back to this Manhwa if you compare their first appearance the oldest doesn't have boobs and her looks is more on the boy side (even wears and looks like a chunibyuu boy). But on her latest appearance she looks like a girl with boobs and her face looks like a girl's. Like how teenager boyish girls are often portrayed in animes
Is the manager’s oldest child a son or daughter?
I assumed son in the beginning, but then translation started mixing up pronouns, and became a child bride.
So boy-ish girl, or boy forced to crossdress??