Like children lined up around worker? (9)
I believe the answer is:
infantile
'like children' is the definition.
(infantile means childish)
'lined up around worker?' is the wordplay.
'lined up' becomes 'in file' (being lined up is being in file).
'around' is an insertion indicator.
'worker?' becomes 'ant' (worker is a type of ant).
'infile' placed around 'ant' is 'INFANTILE'.
(Other definitions for infantile that I've seen before include "Babyish" , "for kids" , "in early stage of development" , "Inflate in childish way" .)