Feeble young child's loose outer garment (7)
I believe the answer is:
paletot
'loose outer garment' is the definition.
(I've seen this before)
'feeble young child's' is the wordplay.
'feeble' becomes 'pale'.
'young child' becomes 'tot' (I've seen this before).
'pale'+'tot'='PALETOT'
(Other definitions for paletot that I've seen before include "coat" , "cloak" , "loose outer garment" , "large overcoat" .)