The word comes from the Latin word for "boy”
Following Donald Trump’s victories on Super Tuesday, New York Times columnist Nicholas Kristof wrote a piece with the title “After Super Tuesday, Bracing for a President Trump”:
Trump has shrewdly manipulated the news media and has proved a much more accurate reader of the electorate than we pundits. Yet I’ve never met a national politician so ill informed, so evasive, so bombastic and, frankly, so puerile.
Puerile means “silly or childish especially in a way that shows a lack of seriousness or good judgment.” It comes from the Latin word for “boy” or “child,” puer. Like many words in English, it originally had a more literal meaning derived from its Latin root: “of or relating to childhood” or “boyish.” Over time, the more figurative use became more common; it usually refers in a disapproving way to childish behavior on the part of adults who should know better.
It also has a specific medical meaning referring to the respiration of a child as in “puerile breathing” (like other Latin-based words with both general meanings and specific medical meanings, such as geriatric as in “geriatric pregnancy” and spastic as in “spastic colon”).
Washington Post columnist Eugene Robinson also used puerile in a column about the GOP primaries.