Writer is on piano annoying child (3)
I believe the answer is:
imp
'annoying child' is the definition.
'imp' can be an answer for 'child' (imp is a kind of child). I am not sure about the 'annoying' bit.
'writer is on piano' is the wordplay.
'writer' becomes 'im' (I've seen this in other clues).
'is on' says to put letters next to each other.
'piano' becomes 'p'.
'im'+'p'='IMP'
Can you help me to learn more?
(Other definitions for imp that I've seen before include "Young troublemaker" , "Small devil or sprite" , "Evil spirit" , "Naughty demon" , "Rascal" .)