Sums up little ones (4)
I believe the answer is:
tots
This clue is a double definition.
'sums up' is the first definition.
('tot' can be a synonym of 'sum up')
'little ones' is the second definition.
(I've seen this in another clue)
(Other definitions for tots that I've seen before include "Adds up for the youngsters" , "Finds the sum" , "Sailors' drams" , "Little drinks" , "Little children" .)