A little reprobate, a selfish kid (5)
I believe the answer is:
tease
'kid' is the definition.
(I've seen this in other clues)
'a little reprobate a selfish' is the wordplay.
'a little' says the answer is hidden in the clue.
'TEASE' can be found hidden inside 'reprobate a selfish'.
(Other definitions for tease that I've seen before include "Pull leg of" , "Torment lightly" , "Page of book" , "Vex" , "Taunt or bait" .)