Denounce dad and mom's new beginnings (4)
I believe the answer is:
damn
'denounce' is the definition.
(I've seen this in another clue)
'dad and mom's new beginnings' is the wordplay.
'beginnings' suggests taking the first letters.
The first letters of 'dad and moms new' is 'DAMN'.
(Other definitions for damn that I've seen before include "Curse; strongly criticise" , "Blast!" , "Consign to hell" , "Condemn as worthless" , "hang" .)