Become very angry on being caught by children (3,3)
I believe the answer is:
see red
'become very angry' is the definition.
(I've seen this before)
'on being caught by children' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'being caught by' indicates putting letters inside.
'children' becomes 'seed' (I've seen this before).
're' inserted into 'seed' is 'SEE RED'.
(Other definitions for see red that I've seen before include "Become angry as bull might" , "Be suddenly angry - like bull?" , "blow a gasket" , "Lose temper as bull might" , "Become angry like bull" .)