US singer beginning to upset writer of sweet innocence? (8)
I believe the answer is:
cherubic
'of sweet innocence?' is the definition.
(innocent as a cherub)
'us singer beginning to upset writer' is the wordplay.
'us singer' becomes 'cher' (US musician Cher).
'beginning to' suggests taking the first letters.
'writer' becomes 'bic' (kind of pen).
The initial letter of 'upset' is 'u'.
'cher'+'u'+'bic'='CHERUBIC'
(Other definitions for cherubic that I've seen before include "like an angel" , "Having a nature befitting an angel" , "Angelic, seraphic" , "Like a child" , "Having a plump innocent face" .)