What may help little person to see fairy's garment (9)
I believe the answer is:
periscope
'what may help little person to see' is the definition.
'fairy's garment' is the wordplay.
'fairy's' becomes 'peris' (Persian mythological being).
'garment' becomes 'cope' (type of religious cloak).
'peris'+'cope'='PERISCOPE'
(Other definitions for periscope that I've seen before include "overseer" , "Submarine's viewer" , "Optical instrument" , "Submarine's viewing tube" , "Viewing instrument in a submarine" .)