Child with a devious brain (5)
I believe the answer is:
bairn
'child' is the definition.
(bairn is a kind of child)
'a devious brain' is the wordplay.
'a devious' is an anagram indicator.
'brain' anagrammed gives 'BAIRN'.
'with' is the link.
(Other definitions for bairn that I've seen before include "Scots child" , "little one in Yorkshire" , "Scot. child" , "Child in Scotland" , "Wee child" .)