Small child’s drink (3)
I believe the answer is:
tot
I believe this clue is a double definition.
'small child's' is the first definition.
(I've seen this before)
'drink' is the second definition.
(I've seen this before)
(Other definitions for tot that I've seen before include "Add up like infant" , "quick drink" , "Small drink of spirits" , "An arithmetic babe?" , "Party drink" .)