Crossword Genius

Get childishly upset (informal) (5,1,6)

Ross

I believe the answer is:

throw a wobbly

(Other definitions for throw a wobbly that I've seen before include "Have a tantrum (colloq.)" , "Have a fit" , "Become very angry" , "Go ballistic" , "Suddenly blow a fuse" .)

I've seen this clue in The Guardian.
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