A child run in for a crime (5)
I believe the answer is:
arson
'a crime' is the definition.
(I've seen this before)
'a child run in' is the wordplay.
'child' becomes 'son' (son is a kind of child**).
'run' becomes 'r' (cricket abbreviation).
'in' means one lot of letters goes inside another.
'a'+'son'='ason'
'ason' placed around 'r' is 'ARSON'.
'for' acts as a link.
(Other definitions for arson that I've seen before include "Criminal burning of property" , "Incendiarism" , "Crime of fire raising" , "Fire-raising crime" , "Iniquitous behaviour" .)