Blow to make naughty child behave (6)
I believe the answer is:
impact
'blow' is the definition.
(thesaurus)
'naughty child behave' is the wordplay.
'naughty child' becomes 'imp' (informal term for a misbehaving child).
'behave' becomes 'act' (as in acting or behaving a certain way).
'imp'+'act'='IMPACT'
'to make' acts as a link.
(Other definitions for impact that I've seen before include "Marked effect or influence" , "Forcible contact between two things" , "Significance" , "Forcible contact; marked influence" , "Forceful striking" .)