Badly-behaved child (4)
I believe the answer is:
brat
'badly-behaved child' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for brat that I've seen before include "A spoiled, badly behaved child" , "Urchin" , "Bad child - pack member!" , "Young rascal" , "annoying young fellow" .)