Kittens' mess (6)
I believe the answer is:
litter
This clue is a double definition.
'kittens'' is the first definition.
(I've seen this before)
'mess' is the second definition.
(thesaurus)
(Other definitions for litter that I've seen before include "issue in the farmyard" , "Little pigs, for example" , "Rubbish strewn about the streets" , "Offspring of a multiple birth" , "Chair or bed carrried on two poles" .)