Mungo

Mungo is the term the children of Little Lamplight use for adults, ever since they were rejected entry into Vault 87 by its (adult)inhabitants. If you talk to some residents of Little Lamplight, they will sing the chant: 'Mungo, Mungo, smells like dung-o!'. People are considered to be Mungos after they reach 16 and are no longer allowed to live in Little Lamplight.

"Mungo" is likely slang for "Humongous," as grown-ups often look quite large to children.

The sign that originally said "Come to Lamplight Caverns" now says "Don't come to Lamplight Caverns, Mungos beware."

The Lamplighters dislike of grown-ups is explained in Holotapes found around the caverns.