Scatter-brain child (5)
I believe the answer is:
bairn
'child' is the definition.
(bairn is a kind of child)
'scatter-brain' is the wordplay.
'scatter' is an anagram indicator.
'brain' with letters rearranged gives 'BAIRN'.
(Other definitions for bairn that I've seen before include "Child (of the North!)" , "Kid" , "Child in Scotland" , "Northern child" , "A tot of Scotch" .)