New brain child (5)
I believe the answer is:
bairn
'child' is the definition.
(Scottish and northern English term for a child)
'new brain' is the wordplay.
'new' is an anagram indicator.
'brain' with letters rearranged gives 'BAIRN'.
(Other definitions for bairn that I've seen before include "Scot. child" , "Child in Scotland" , "Northern child" , "Kid" , "Scots child" .)