Infantile

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late Middle English: from French, or from Latin infantilis, from infans, infant- (see infant).

wiktionary

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Mid-15th century, "pertaining to infants," from Latin infantilis(“pertaining to an infant”), from īnfāns. Sense of "infant-like" is from 1772. [1]

etymonline

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infantile (adj.)

mid-15c., "pertaining to infants," from Late Latin infantilis "pertaining to an infant," from infans "young child" (see infant). Sense of "infant-like" is from 1772.