Young kittens? Rubbish! (6)
I believe the answer is:
litter
This clue is a triple definition!
'young' is the first definition.
(thesaurus)
'kittens?' is the second definition.
(I've seen this before)
'rubbish' is the third definition.
(I know that litter is a type of rubbish)
(Other definitions for litter that I've seen before include "Trash left lying about" , "Chair or bed carried on two poles" , "Not a neat" , "Scattered rubbish" , "Rubbish strewn about the streets" .)