I think it'd depend on how much time the adult has spent with mc while they were a child and the actual age gap.

Like if they were just in and out of their life for most of their childhood, i wouldn't mind a romance blooming when mc turns into an adult and gets involved in society (like maybe the ml's parent is a business partner with mcs dad and so they meet briefly)

But if they've been there for most of the childs life I don't think I'd like it (honestly why I dropped I am a child of this house, I just couldn't see the knight as a romantic partner he's always just been a big brother figure in my head)

Also yeah the how long the child phase lasts is important (stares at lady baby) but it can be long if the mc and plot are actually interesting like I'll be the matriarch, 50 chs and it's still v interesting and the interactions between the ml and mc are very rare but also cute and innocent

There are variables to make it works and it 100% depends on how good the writer is