To be fair, in the Anime / Manga itself, the really old man / woman that looks like a child is more played for laughs. It's the community that sexualizes the character, not the actual show / comic.
Usually. Then there's fantasy settings with halflings and dwarves and such, but they look more like adult humans with smaller bodies. Finn Deimne from Danmachi coming to mind, as he's an actual halfling hero and basically the leader of his troop. Has a full sized human woman after him, but I feel like it's not weird, as they're both adults. Just adults of different sizes / races.