Rabbit, soft baby's toy (7)
I believe the answer is:
prattle
'rabbit' is the definition.
(I've seen this before)
'soft baby's toy' is the wordplay.
'soft' becomes 'p' (musical abbreviation for 'piano').
'baby's toy' becomes 'rattle' (I've seen this before).
'p'+'rattle'='PRATTLE'
(Other definitions for prattle that I've seen before include "Chatter inconsequentially, natter" , "rabbit" , "Inconsequential chatter" , "Foolish talk" , "Chat inconsequentially" .)