First it was the mass genocide of civilians in the predecessor, and now it's the death of a child due to an exploding truck in Modern Warfare 3. We're sitting in anticipation for this one to raise the mass concern among the British press.
The scene shows a Father taking a video recording of his wife and daughter, as they talk about the day out they had planned. The little girl wanders off slightly, a truck pulls up, men run out of it and then it explodes.
There is the keen ideal to relate this to the airport scene from the "No Russian" level in Modern Warfare 2; but to the counterpoint of this, instead of being left with a choice to kill innocents or not, this plays out like a cutscene, so you play no part in harming anyone or anything.
Children dying in a sudden fashion as this is a ploy that's been used everso fondly as of recent by the film industry, using the subtext of the event to instantly paint one set of people as evil. It absolutely defines the good guys from the bad. However, to video games, this is a new plot device, and this new-ness of interactive entertainment taking advantage of this subconcious story setter is probably why newspapers are going to have a field day with this.