Bit of a lark, I dare say, for a youngster (3)
I believe the answer is:
kid
'a youngster' is the definition.
(I know that youngster can be written as kid)
'bit of a lark i dare say' is the wordplay.
'bit of' indicates the answer is hidden within the clue.
'KID' is hidden in the letters of 'lark i dare say'.
'for' is the link.
(Other definitions for kid that I've seen before include "In slang, young child or goat" , "little one" , "Goat - boy" , "Pretend" , "Joke" .)