Occasionally noted aberrant child is excessively unruly (4)
I believe the answer is:
brat
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for brat that I've seen before include "Mervyn -- (Titus Groan)" , "Horrible child" , "Unpleasant child" , "Ill-mannered child" , "Marie ---, birth-control pioneer" .)