A tot of Islay or Loch Lomond? (5)

I believe the answer is:

bairn

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'a tot' is the definition.
(I have seen 'tot of Scotch' mean 'bairn' so perhaps 'tot' could also mean 'bairn')

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for bairn that I've seen before include "Child in Scotland" , "Scots child" , "Northern child" , "Kid" , "Child (of the North!)" .)

I've seen this clue in The Times.

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