Lad beginning to grow emphasises such performers (12)

'performers' is the definition.
(songstress is a kind of performer)

'lad beginning to grow emphasises' is the wordplay.
'lad' becomes 'son'.
'beginning to' suggests taking the first letters.
'emphasises' becomes 'stresses' (stress is a kind of emphasis).
The first letter of 'grow' is 'g'.
'son'+'g'+'stresses'='SONGSTRESSES'

'such' is the link.