Bungling mother and boy performing trio (9)
I believe the answer is:
maladroit
'bungling' is the definition.
(similar in meaning)
'mother and boy performing trio' is the wordplay.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'and' is a charade indicator (letters next to each other).
'boy' becomes 'lad' (informal term for boy).
'performing' indicates anagramming the letters.
'trio' is an anagram of 'roit'.
'ma'+'lad'+'roit'='MALADROIT'
(Other definitions for maladroit that I've seen before include "Inept, clumsy" , "Awkward - unskilful" , "Inefficient, clumsy" , "Clumsy or bungling, ham-fisted" .)