Mainly - how do you react to a child who over reacts so out of proportion the moment it happens when he/she seems so hard to reach and so caught in the moment and emotions?
(me again, lol)
Ok for these moments specifically (been there many times, with both kids) this is what I do:
-I remove them from whatever environment they're in (I've had to drag my son away from the school playground, for example). At home we either stay put or go to another room if friends are present.
-I wait a minute or so to let them process their feelings. This is particularly important with DS8 - I have to let him "tantrum" for a minute or two before I have any hope of reaching him.
-I get down to his/her level so that my face is close to theirs. The reason is that I need them to hear me, and if I shout over the meltdown, it's harder to calm it down.
-I use a firm, calm, slow and strong voice and talk. "Calm yourself down. Use words and tell me why you're upset." etc etc.
Because of my son's language processing disorder, this is sometimes hard. When he gets upset, the language part of his brain just seizes up. So then I'll guess, and he'll nod or shake his head yes or no: "Are you upset because you want a turn with the Wii? No? Are you upset because ___ won't let you help him? Ok. Sometimes people need to figure things out themselves."
Anyway, the keys I've found are: the wait period, and my voice. If my voice is low, they need to quiet themselves to hear me. Once they're engaged in listening, I can out-logic the tantrum.
I hope that helps... good luck