Gets going on the small pastries (6)
I believe the answer is:
starts
'gets going' is the definition.
('start' can be a synonym of 'get going')
'on the small pastries' is the wordplay.
'on' says to put letters next to each other.
'the small' becomes 's' (abbreviation - e.g. clothes size).
'pastries' becomes 'tarts' (tart is a kind of pastry).
's'+'tarts' is 'STARTS'.
(Other definitions for starts that I've seen before include "Begins or causes to begin" , "Begins with surprise reactions?" , "Commences" , "Begins or makes sudden movement as from surprise" , "origins?" .)