Rotten time of year for children (9)
I believe the answer is:
offspring
'children' is the definition.
(thesaurus)
'rotten time of year' is the wordplay.
'rotten' becomes 'off' (I've seen this before).
'time of year' becomes 'spring' (spring is a kind of time of year).
'off'+'spring'='OFFSPRING'
'for' is the link.
(Other definitions for offspring that I've seen before include "Progeny" , "Child" , "Kids" , "Young" , "Children, issue" .)