Youngster I left with daughter after church (5)
I believe the answer is:
child
'youngster' is the definition.
('child' can be a synonym of 'youngster')
'i left with daughter after church' is the wordplay.
'left' becomes 'l' (common abbreviation**).
'with' means one lot of letters go next to another.
'daughter' becomes 'd'.
'after' is a charade indicator (letters next to each other).
'church' becomes 'ch' (common abbreviation).
'i'+'l'='il'
'il'+'d' is 'ild'.
'ild' put after 'ch' is 'CHILD'.
(Other definitions for child that I've seen before include "Offspring" , "Not an adult" , "Infant" , "Minor" , "Immature human" .)