Leaving out with son asleep (8)
I believe the answer is:
skipping
'leaving out' is the definition.
(skipping is a kind of leaving out)
'with son asleep' is the wordplay.
'with' is a charade indicator (letters next to each other).
'son' becomes 's' (genealogical abbreviation for son).
'asleep' becomes 'kipping' (kip can mean to sleep).
's'+'kipping' is 'SKIPPING'.
(Other definitions for skipping that I've seen before include "Jumping with a rope" , "Cutting" , "Playing with a rope" , "amusement" , "Jumping lightly or bypassing" .)