That looks and sounds terrible, its been a long time since there has been a crash like that, must have been hideous for all involved, devastating, a bad RTC on a motorway, involving trapped, in fires and more than likely children, it doesn't get any worse than that.
I agree with the comments about bad driving, but most of the time what causes a lot of crashes is doing something other than concentrating on driving, letting other things distract you, I've lost count of the times we have found things in the drivers foot well at crashes, as Dude says lane discipline and distance are 2 of the worst things on a motorway.
That's my two penneth anyway, my feelings go out to all involved, this will change a lot of lives forever.