Copper with brass edges for youngsters (4)
I believe the answer is:
cubs
'for youngsters' is the definition.
(cub can mean a baby or child)
'copper with brass edges' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'with' says to put letters next to each other.
'edges' says to hollow out the word (remove centre letters) (I've seen 'edges of' mean this).
'brass' with its centre taken out is 'bs'.
'cu'+'bs'='CUBS'
(Other definitions for cubs that I've seen before include "Whelps" , "Junior Scouts" , "Young and inexperienced reporters" , "Little foxes" , "Young wolves" .)