It’s often assumed that when babies say mama or papa (or similar) they are addressing or referring to their mother or father explicitly. Not so. In a 2012 post on mama/papa words around the world, I wrote:
Before I knew anything about language acquisition, I assumed that babies making these utterances were referring to their parents. But this interpretation is backwards: mama/papa words just happen to be the easiest word-like sounds for babies to make. The sounds came first – as experiments in vocalization – and parents adopted them as pet names for themselves.
These pet names, or nursery forms, in turn gave rise to our grown-up terms like mother and father – or rather, their ancient predecessors – according to Roman Jakobson’s 1959 paper ‘Why “Mama” and “Papa”?’ (PDF). The striking correspondence of nursery forms cross-lingually can be seen in a table from Larry Trask’s ‘Where do mama/papa words come from?’ (PDF):
The Great Language Muster is a project collecting data from hundreds of languages in an effort to update our knowledge of these and other kinship terms – how we address and refer to parents, grandparents, aunts, and uncles. It’s being run by UCL linguistics professor Andrew Nevins, whose research assistant Evan DeFrancesco emailed me about it.