New woman with head of year - a children's nurse (5)
I believe the answer is:
nanny
'a children's nurse' is the definition.
(I've seen this before)
'new woman with head of year' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'woman' becomes 'ann' (woman's name).
'with head of' indicates taking the first letters.
The initial letter of 'year' is 'y'.
'n'+'ann'+'y'='NANNY'
(Other definitions for nanny that I've seen before include "Spoon-feed" , "Undue government interference with personal choice?" , "Children's nurse" , "Producer of milk" , "One looking after children" .)