Parent of boy who's a rascal? (3)
I believe the answer is:
gun
'parent of boy' is the definition.
'Gun' can be an answer for 'boy'. I'm not sure about the 'parent of' bit.
I cannot understand how the remainder of the clue works.
(Other definitions for gun that I've seen before include "Hired killer" , "Shooter" , "Platform from which to shoot" , "An offensive weapon" , "Throttle" .)