Young animal has favourite toy (6)
I believe the answer is:
puppet
'toy' is the definition.
(I know that puppet is a type of toy)
'young animal has favourite' is the wordplay.
'young animal' becomes 'pup' (I've seen this in another clue).
'has' is a charade indicator (letters next to each other).
'favourite' becomes 'pet' (synonyms).
'pup'+'pet'='PUPPET'
(Other definitions for puppet that I've seen before include "Pawn - marionette" , "Small figure of a person operated with strings" , "Small doll on strings" , "Pinocchio, e.g." , "Doll controlled by strings" .)