Meltdowns are not tantrums.
I'll say that again: Meltdowns are not tantrums.
Why should anyone care about the difference? Because although they may look the same to the untrained eye, the cause of and appropriate response to each are vastly different.
In our little world, Son #1 has meltdowns, while Son #2 used to throw tantrums. Notice how I can discuss tantrums in the past tense, while meltdowns remains in the present tense? That is because tantrums are cries for attention, which can be redirected into more positive ways of communicating. Meltdowns are reactions to sensory overloads, which can sometimes be circumvented ahead of time, but are nearly impossible to stop once fully underway.
Let me give an example of a typical tantrum Son #2 used to have. When he was pre-verbal (see Which Came First: The Speech Delay or the Creativity?), Son #2 used to get very angry when I was cooking dinner. The smells of food would drive his stomach into overdrive, and he wanted to eat now. Since I didn't want him filling up before dinner, I would tell him to wait, that dinner would be ready in 20 minutes, ask if he wanted to help, etc. He would simply stand there and scream at me with every bit of energy and power his little body could produce. I finally came up with the rule "No screaming at Mom in the kitchen." I would pick him up, state the rule, and put him in the living room. The first few times, he was surprised. Then he apparently spent sometime parsing the language of the rule, searching for the legal loophole. Of course, being two years old, he found it. Instead of screaming at me in the kitchen, he would calmly walk out, turn around, put his toes right at the edge of the entrance, and begin screaming. Technically, he wasn't in the kitchen, so he was obeying the rule. No "spirit of the law" for a two-year-old.
Now, let's review one of Son #1's meltdowns. The scene: his brother's birthday party, filled with kids of all ages running wild in our yard. The party was scheduled for three hours, but one friend arrived early and many stayed late. We love hanging out with our friends, so we were fine with this; but Son #1 needed a break, and there was nowhere to hide. He seemed to be managing all right, but when a beach ball that we got at a science open house from Berkeley Labs was accidentally burst, he exploded. One of the moms, who is very patient and gentle, was talking to him, but I could see his body language: stiffness, gritted teeth, intensity radiating from every pore. A meltdown was on the way, and it wasn't going to be pretty. I went over to him, held him, and he erupted in a wave of tears and wrath-filled accusations. His body went limp, and it was all I could do to get him to a bench. We sat down and I just held him as he poured out his anger and hurt and frustration. Once he was calm enough to hear me (he cannot process what I say when he's in the middle of a meltdown), we could talk about what had happened and get him functioning enough to go lie down on his bed. He wasn't over the upset, just worn out. At this point, I'm exhausted, he's exhausted, and the other parties are in shock. Son #1's meltdowns are nuclear explosions compared to the car-backfirings of Son #2's tantrums.
I believe that the tantrum habit can be broken. Often, tantrums are a cry for attention. The child might be hungry, tired, scared, overwhelmed, or the child might have learned that throwing a tantrum gets him what he wants. Being firm and loving will go a long way to ending the tantrums.
Meltdowns, on the otherhand, are an existential scream at the "too muchness" of the world. Too much sound, too much touch, too many people, too much of the wrong food, too much everything. Love and compassion are required, but discipline, in the moment, is useless. Maybe the child needs to be held. Maybe he needs to be left alone in a safe environment. Regardless, the child and the parents need love and compassion.
On a related note, Son #1 informed me a couple of weeks ago that, now he's getting older, he can periodically feel hormone surges. Buckle your seatbelts. Check those safety harnesses, folks. The next few years are going to be one wild ride!