Offspring of a rock idol (3)
I believe the answer is:
kid
'offspring' is the definition.
(kid is a kind of offspring)
'of a rock idol' is the wordplay.
'of' indicates a hidden word.
'KID' is hidden within 'a rock idol'.
(Other definitions for kid that I've seen before include "Soft leather" , "Sort of glove" , "Josh" , "Jest" , "Young animal or child" .)