The last section by naughty child is about to happen (9)
I believe the answer is:
impending
'about to happen' is the definition.
(I've seen this before)
'the last section by naughty child' is the wordplay.
'the last section' becomes 'ending' (ending is a kind of section. I am not sure about the 'last' bit.).
'by' means one lot of letters go next to another.
'naughty child' becomes 'imp' (informal term for a misbehaving child).
'ending' put after 'imp' is 'IMPENDING'.
'is' is the link.
Can you help me to learn more?
(Other definitions for impending that I've seen before include "About to happen" , "Looming" , "Threatening" , "coming?" .)