Whiny kid (4)
I believe the answer is:
brat
'whiny kid' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for brat that I've seen before include "Ill-mannered child" , "Marie ---, birth-control pioneer" , "Annoying child" , "Nasty child" , "Young rascal" .)