The Spanish word "niño" (meaning "child") comes from Old Spanish "ninno", which in turn derives from Late Latin "ninnus". "Ninnus" was a nursery word or baby-talk term for "child" in Late Latin. This is a great example of how words used in baby talk or child-directed speech can become standard vocabulary in a language over time. The evolution from "ninnus" to "ninno" to "niño" shows typical sound changes in Spanish, including the development of the Spanish letter ñ (pronounced like 'ny').

Some common related Spanish words include "niñez" (childhood), "niñera" (nanny/babysitter), and the diminutive "niñito/a" (little child). All these words maintain the core meaning related to children or childhood.

While English doesn't have any direct cognates from the Latin "ninnus", we do have some words that serve a similar function as nursery words for children, like "tiny" and "wee". However, these have different etymological origins. The closest connection might be in how we use "nin-" in words like "ninny" (a foolish person), which some etymologists suggest might be related to the childish associations of the Latin root, though this connection is uncertain.