Sum for child, adding one and fifty (5)
I believe the answer is:
total
'sum' is the definition.
(I know that sum can be written as total)
'child adding one and fifty' is the wordplay.
'child' becomes 'tot' (term for a young child).
'adding' is a charade indicator (letters next to each other).
'one' becomes 'a' (a thing is one thing).
'and' says to put letters next to each other.
'fifty' becomes 'l' (Roman numeral).
'tot'+'a'+'l'='TOTAL'
'for' is the link.
(Other definitions for total that I've seen before include "final answer" , "Count" , "Aggregate, sum" , "Completely destroy" , "Entirety" .)