Plant that stings adults cuts little child (5-2-3)

'plant' is the definition.
(touch-me-not is a kind of plant)

'that stings adults cuts little child' is the wordplay.
'that stings' becomes 'ouch' (that hurts!).
'adults' becomes 'men' (men are adults).
'cuts' means one lot of letters goes inside another (some letters cut their way into a word).
'little child' becomes 'tot' (informal term for a young child).
'ouch'+'men'='ouchmen'
'ouchmen' put inside 'tot' is 'TOUCH-ME-NOT'.