Child is a girl (5)
I believe the answer is:
issue
'child' is the definition.
(I've seen this before)
'is a girl' is the wordplay.
'a girl' becomes 'sue' (girl's name).
'is'+'sue'='ISSUE'
(Other definitions for issue that I've seen before include "The children to come forth" , "Children; topic for debate" , "Progeny of, send out" , "Publish - put into circulation" , "Important question" .)