Child is involved in trickery for criminals (9)
I believe the answer is:
arsonists
'criminals' is the definition.
(arsonist is a kind of criminal)
'child is involved in trickery' is the wordplay.
'child' becomes 'son' (son is a kind of child).
'involved' is an insertion indicator.
'in trickery' becomes 'arts' (I can't explain this - if you can you should believe this answer much more).
'son'+'is'='sonis'
'sonis' going into 'arts' is 'ARSONISTS'.
'for' is the link.
Can you help me to learn more?
(Other definitions for arsonists that I've seen before include "people with a burning desire" , "Criminals" .)