One politician's naughty children (4)
I believe the answer is:
imps
'naughty children' is the definition.
(I've seen this before)
'one politician's' is the wordplay.
'one' becomes 'i' (Roman numeral).
'politician's' becomes 'MP's' (Member of Parliament).
'i'+'mps'='IMPS'
(Other definitions for imps that I've seen before include "repairs (for a wing)" , "Demons" , "Mischievous fairies" , "naughty children" , "Small devils or mischievous children" .)