Youngster or pincer (6)
I believe the answer is:
nipper
This clue is a double definition.
'youngster' is the first definition.
(I know that youngster can be written as nipper)
'pincer' is the second definition.
(synonyms)
(Other definitions for nipper that I've seen before include "Informal young child or lobster claw" , "guilty of pinching?" , "Claw (large) - child (small)" , "young one" , "Little kid" .)