If one of them is having a complete meltdown, screaming tantrum over something I just really suddenly with no warning make the music really loud. It shocks them into shuttingup calming down immediately.
I explain it to them as if there has to be a really loud noise I'd rather hear the radio than them.
My older dd and her friend once filmed my toddler in mid tantrum/meltdown on her mobile. Now whenever she is in mid scream, we show her the clip again and she immediately shuts up cos she is so very impressed.
All the dcs in the back, me going absolutely nuts with the whining and complaining, so I turned Radio4 on and was greeted with the - expected - chorus of "That's boring" and "I want my music" and "WAAAAAAAAAAA". I could feel the volcano about to erupt in my head, so, rather than shriek at the little demons darlings, or just crash, I cranked the volume unpleasantly high.
Instant peace and quite behind. Gradually turned the volume down over the next mile or two, and enjoyed the 20min drive listening to dear darling Radio 4.
Chirldren surprisingly polite and placid on arrival, too!
Hmm, Innacity Hip Hop music (at normal volume as opposed to eardrum bursting volume) seems to work well on my 8 month old - discovered by total accident while tuning the radio while he was having a major paddy. DS1 was into greek balalyrka music (on greek orthodox london radio) as his sure fire trick to stop him crying as a baby. Small people have the wierdest tastes. Thought would share in case it helps anyone trpped in a car with screaming tiny people...