'bairn' originates from Old English, specifically the word 'bearn', where 'bearn' meant 'child'.

'bairn' evolved from Old English 'bearn' (and Middle English northern forms such as 'barn'/'bairn'), and was retained in Scots and northern English dialects as the modern form 'bairn'. It is also cognate with other Germanic words such as Old Norse 'barn' and modern Scandinavian 'barn' meaning 'child'.

Initially, it meant 'child', and over time this basic meaning has largely remained unchanged into the modern dialectal use of 'bairn'.