In Ancient Greek, diminutives are almost always neuter, regardless of the original noun's gender. This leads to words like paidíon, "small child" (from país "child"), which are neuter even though they refer to people.
In modern German, the same thing happens: Mädchen "girl" (from Magd "young woman") is neuter rather than feminine.
But in Latin, I can't think of any word for an individual human that's not masculine (puer), feminine (femina), epicene(*) (homo), or common(*) (ruricola).
Does any such noun exist? That is, is there any noun that unambiguously refers to an individual human being, but is grammatically neuter?
(*) As Alex B puts it, epicene nouns are fixed as grammatically masculine or feminine, but can refer to a male or female person: a good person, man or woman, is a homo bonus. Common nouns are masculine when referring to a male person and feminine when referring to a female person: a good country-dweller is a ruricola bonus or a ruricola bona.