I know this is a genre staple and a common exploration in a lot of fantasy/adventure/coming-of-age type stories. But I really do love the specific poignancy of how LOZ explores the feeling of being too young and small to be significant in the eyes of the people around you.
Ocarina of Time is pretty direct about the things Link can do specifically because he is a child, even forcing Link to go back in time post-timeskip to revisit his younger self. Some of this is time travel fuckery, but sometimes it's just as simple as, "An adult can't fit through this very small passageway." There's ups and downs to taking up more space in the world, the autonomy of adulthood vs the freedom of being invisible.
In Majora's Mask, Link's first significant marker of functional adulthood is not his changing body, but obtaining a weapon, which is a visual signal that changes everyone else's perception of him to match what we already know is inside (someone who has already survived very adult experiences). Like Ocarina of Time, this adulthood is reversible. Even after Link starts carrying a sword, he's still small enough that people don't notice until he draws attention to it. Even after he assumes full-grown Zora and Goron forms, he can choose to shed those forms when he pleases. He can still slip under the radar as a 'child' - adults freely have conversations with him, or around him, with the assumption that he won't fully understand them. The appearance of adulthood grants Link access to the wilds of Termina, & the appearance of childhood grants him access to information and relationships in the world of Clock Town.
Again, lots of stories do explore this same theme, but to me the ending of OoT just hits somewhere really deep. Link and Zelda are both scarred and robbed of childhood. (A parallel here between Adult Link and Sheik - neither Link nor Zelda were allowed to grow up naturally, instead forced to adopt bodies more suited to the adulthood required of them.) Zelda so badly wants to fix it, to make things right by at least giving Link his own childhood back - even if she can't have hers - but neither of them actually had a childhood in the first place. Link grew up alienated from his peers as an outsider, and then the physical state of being a child became just another tool in his arsenal. Zelda grew up burdened by status and the crushing weight of prophecy. There's nothing to 'give back' because it didn't exist.
Majora's Mask makes this so explicit by starting the game off cursing Link into Deku form, putting him in a tiny body that constrains him and initially presents only limitations and frustrations. Zelda's aching, misguided kindness and Skull Kid's malice have the same functional outcome, and in some ways, the same root: Zelda's naive, desperate desire to help and Skull Kid's petty tantrums are both emotions associated with childishness.
There's other aspects to go into for another day. The fact that Link is always a villager, or a goatherd, or a soldier. The way that Link waking up in BOTW to a world that has moved on without him grants him a similar kind of functional invisibility. And of course the Hero's Shade in Twilight Princess: finally fully grown, powerful, a mentor, but stripped back to bones and hidden in shroud.
