Crows start to bite kids (5)
I believe the answer is:
brags
'crows' is the definition.
('brag' can be a synonym of 'crow')
'start to bite kids' is the wordplay.
'start to' suggests taking the first letters.
'kids' becomes 'rags' (I've seen this before).
The first letter of 'bite' is 'b'.
'b'+'rags'='BRAGS'
(Other definitions for brags that I've seen before include "Crows" , "Boasts" .)