Unless you have perfect children, my girls can be very dramatic at times but don't all kids have their moments no matter how great they are?  I have done everything the "right" way to help them stay calm but I have found that breathing techniques work best when my 5 yr old and 2 1/2 yr old get really worked up. We do it together and I get down to their level face to face and we try to take deep breaths together while we look at each other eye to eye.  Once we are calm enough, then we talk out the situation.  It helps my kids learn how to calm down on their own if I am not around.