Coming into a little money benefits youngster (10)
I believe the answer is:
adolescent
'youngster' is the definition.
(thesaurus)
'coming into a little money benefits' is the wordplay.
'coming into' is an insertion indicator.
'little money' becomes 'cent' (I've seen this before).
'benefits' becomes 'doles' (dole can informally mean a government benefit).
'a'+'cent'='acent'
'acent' enclosing 'doles' is 'ADOLESCENT'.
(Other definitions for adolescent that I've seen before include "Immature" , "Person in child-adult transition" , "juvenile" , "Developing" , "Youngster" .)