Office and flats converted for the birds and the bees (5,2,4)
I believe the answer is:
facts of life
'the birds and the bees' is the definition.
(I've seen this before)
'office and flats converted' is the wordplay.
'and' is a charade indicator (letters next to each other).
'converted' indicates an anagram.
'office' put after 'flats' is 'flatsoffice'.
'flatsoffice' is an anagram of 'FACTS OF LIFE'.
'for' acts as a link.
(Other definitions for facts of life that I've seen before include "Information on procreation" , "Essential knowledge for teenagers?" , "The birds and the bees" , "Realities" .)