Second child is married, creating a rift (6)
I believe the answer is:
schism
'a rift' is the definition.
(I've seen this before)
'second child is married' is the wordplay.
'second' becomes 's' (common abbreviation).
'child' becomes 'ch'.
'married' becomes 'm'.
's'+'ch'+'is'+'m'='SCHISM'
'creating' acts as a link.
(Other definitions for schism that I've seen before include "Split, rift" , "Splinter group" , "Breach or division within church" , "Belief-led division" , "Split in religious body over differences in beliefs" .)