Mother Brown's little boy? (4)

I believe the answer is:

herb

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'boy?' is the definition.

'mother brown's little' is the wordplay.
'HERB' is hidden in amongst the letters.
But, I'm uncertain how this is indicated.

Can you help me to learn more?

(Other definitions for herb that I've seen before include "Aromatic plant used in cookery" , "plant with useful properties" , "Medicinal or culinary plant" , "Useful or edible plant" , "Simple" .)

I've seen this clue in the Evening Standard.

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