Youngster's outfit nurse cut short (6)
I believe the answer is:
kitten
'youngster's' is the definition.
(I've seen this before)
'outfit nurse cut short' is the wordplay.
'outfit' becomes 'kit' (kitting is a kind of outfiting).
'nurse' becomes 'tend' (tend can mean to nurse or look after).
'cut short' means to remove the last letter.
'tend' with its last letter removed is 'ten'.
'kit'+'ten'='KITTEN'
(Other definitions for kitten that I've seen before include "Little feline" , "Young rabbit" , "Young feline animal" , "Mini-mog?" , "Little mewing ball of fur?" .)