Child worn out before midnight coming to (9)
I believe the answer is:
totalling
'coming to' is the definition.
(I've seen this before)
'child worn out before midnight' is the wordplay.
'child' becomes 'tot' (term for a young child).
'worn out' becomes 'allin' (I've seen this in another clue).
'before' is a charade indicator (letters next to each other).
'midnight' becomes 'g' (the middle letter in 'night').
'tot'+'allin'+'g'='TOTALLING'
(Other definitions for totalling that I've seen before include "Summing to" , "Addition" , "Coming to" .)