Annoying child (4)
I believe the answer is:
brat
'annoying child' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for brat that I've seen before include "Brash young type" , "Ill-behaved child" , "Nasty little kid" , "Irritating youngster" , "Spoilt kid" .)