Spoil no child with a tree variety (10)
I believe the answer is:
adulterate
'spoil' is the definition.
(I've seen this before)
'no child with a tree variety' is the wordplay.
'no child' becomes 'adult' (I've seen this before).
'with' is an insertion indicator.
'variety' is an anagram indicator.
'tree' with letters rearranged gives 'erte'.
'a' inserted within 'erte' is 'erate'.
'adult'+'erate'='ADULTERATE'
(Other definitions for adulterate that I've seen before include "Debase by mixing with something inferior" , "Spoil" , "add inferior material?" , "Contaminate" , "Reduce purity" .)