Idioms are often tested in my country’s Primary School Leaving Exam. So, I have a vested interest in using them in front of my students so that they absorb idioms into their repertoire of words.
Another reason is that I find that they lack the stamina to sustain their attention for a one-hour lesson. So, I thought that a fun brain break would be idiom-related dingbats. Stuff like let the cat out of the bag. Show a dingbat to them and see if anyone manages to figure it out.
Which leads to this question: do you use idioms in your everyday life? If so, what? Foreign idioms are more than welcome!