Dance-pop band playing for new partner's child (7)
I believe the answer is:
stepson
'new partner's child' is the definition.
(son of a new partner)
'dance-pop band playing' is the wordplay.
'dance-pop band' becomes 'Steps' (UK pop group).
'playing' becomes 'on'.
'steps'+'on'='STEPSON'
'for' acts as a link.
(Other definitions for stepson that I've seen before include "Relation, not by blood" , "No pests about this relation by marriage" , "partner's sprog" , "Child from a spouse's former marriage" , "Male child of spouse by earlier marriage" .)