Boy with vacant expression is loaded (5)
I believe the answer is:
laden
'is loaded' is the definition.
(I've seen this before)
'boy with vacant expression' is the wordplay.
'boy' becomes 'lad' (lad is a kind of boy**).
'with' is a charade indicator (letters next to each other).
'vacant' suggests removing the centre.
'expression' with its centre taken out is 'en'.
'lad'+'en'='LADEN'
(Other definitions for laden that I've seen before include "Heavily loaded" , "Burdened, loaded" , "Filled (with)" , "fully charged" , "Like many a cargo ship" .)