Youngster with some weak ideas (3)
I believe the answer is:
kid
'youngster' is the definition.
('kid' can be a synonym of 'youngster')
'some weak ideas' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'KID' is hidden in the letters of 'weak ideas'.
'with' is the link.
(Other definitions for kid that I've seen before include "Soft leather" , "Jest" , "Josh" , "Suede" , "A baby goat or informal child" .)