Woman in US city, one looking after children (5)
I believe the answer is:
nanny
'one looking after children' is the definition.
(someone paid to mind one's children)
'woman in us city' is the wordplay.
'woman' becomes 'ann' (woman's name).
'in' indicates putting letters inside.
'us city' becomes 'ny' (short for New York).
'ann' inserted inside 'ny' is 'NANNY'.
(Other definitions for nanny that I've seen before include "butter" , "Overprotective government deplored by Thatcher" , "Undue government interference with personal choice?" , "Issue tender" , "Posh child minder or female goat" .)