You shouldn’t drop this group of baby mammals (6)
I believe the answer is:
litter
'you shouldn't drop this group of baby mammals' is the definition.
The answer and definition can be both groups as well as being singular nouns.
Maybe there's an association between them I don't understand?
This is the entire clue.
Can you help me to learn more?
(Other definitions for litter that I've seen before include "Refuse - to give birth" , "Brood of young born to an animal" , "dropped by a new dam, perhaps?" , "Rubbish strewn about the streets" , "Refuse; brood" .)