The car the used for this scene had a camera that hung down from the "roof" and could rotate 360 degrees. What resulted was an extremely complicated and highly emotional death of a main character all capture with little to no edits.
Another impressive long take which I think beats out Children of Men, due to the level of complexity required from every actor on screen, is from a Hong Kong film called Hard Boiled. I put the clip in the post and its definitely worth the 3 minute watch because the choreography between the camera man and the actors is pure genius. Plus all the fake guns going off and squibs to match must have been a difficult time for the special effects team because we see people getting "shot" at very unflattering angles.
I'm jealous of the one takes I'm going to be honest. The best one takes are usually the ones you don't notice are happening. Like most things in cinema, this is the goal to make it look as natural as possible.
I included a compilation of impressive long takes. They don't include the entire take but definitely capture the essence and scope of each one.