Yesterday I gave you all a challenge to demonstrate the existence of a Vulgar Latin language, a nearly-unattested state of Latin that existed between Classical Latin (the Latin of ~50 BCE) and the Romance languages. There were five comparative reflexes, but one of the five was evidently lost in the Classical Latin period, and replaced with other Vulgar Latinisms. The result is that the different regional Latin dialects across the Roman Empire selected replacement words from the language.
|Romance words for "child"|
|infans||French enfant||Occitan enfant||Romansch uffant|
|*ninus||Galician neno||Spanish niño||Catalan nen|
|Proto-Slavic *kopylŭ||Romanian copil|
The Classical Latin word was liber, but this was evidently lost early on. It probably had a popular replacement in Vulgar Latin *ninus, perhaps beginning as a slang term. It is found in both Western and Sardinian branches of the Romance family, so its origins must have been very early, but it has sporadic attestation. Portuguese borrowed from Latin creantia while Gallo-Romance languages probably preferred Latin infans. Importantly and exceptionally, the Gallo-Romance language of Catalan uses nen from *ninus, which demonstrates just how popular *ninus was.
The word was replaced by slang in Italian: bimbo, from earlier bambo, probably imitative of a child's speech. Romanian copil was a borrowing from Proto-Slavic, which was once a popular Balkan term for a child. The fact that borrowing and replacement was so prevalent is a strong clue as to the nature of Vulgar Latin.