Barbara rings Yankee — it’s to mind infant (4-3)
I believe the answer is:
baby-sit
'mind infant' is the definition.
(to watch or mind an infant)
'barbara rings yankee it's' is the wordplay.
'barbara' becomes 'Babs' (short for Barbara).
'rings' is an insertion indicator.
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'it's' becomes 'it' (I've seen this in other clues).
'babs' enclosing 'y' is 'babys'.
'babys'+'it'='BABY-SIT'
'to' acts as a link.
(Other definitions for baby-sit that I've seen before include "Relieve parents" , "Tend" , "Look after children temporarily" , "Look after young children" , "Mind small children while parents have a night out" .)