In between small and sweet (4)
I believe the answer is:
twee
'small and sweet' is the definition.
(I've seen this before)
'in between' is the wordplay.
'in' indicates a hidden word.
'TWEE' is hidden in the letters of 'between'.
(Other definitions for twee that I've seen before include "Excessively quaint" , "Overly sentimental or pretty" , "Excessively sentimental" , "Excessively cute" , "Sentimental, quaint" .)