"What has the make of her car got to do with the price of fish?"
These cars are like tanks, they are high up, they are heavy, and they are very powerful. There's a big difference between an Audi Q7 and a Reliant Robin.
Collision testing shows that when a big car impacts with a smaller one, the occupants of the smaller vehicle are much more likely to die.
The witness reports the same, that the kids might have died in a less imposing vehicle. And perhaps it affects the psychology also. Isn't it the plot of a Simpsons' episode? Marge gets one of these things and develops road rage?