I haven't seen Children of men but there was a movie shot a few years ago to look like a single take. They really did it in numberous takes and edited them together the way you're suggesting. The camera would move behind someone creating an instant of blackness (doesn't require the whole screen to be black at once) that would be used for the edit line. Pillars. A flashbulb. Anything like that. I imagine that a bit of fast motion and blending of flames would be hard to notice if your shot appeared to be going through a window or wall.

RJSchwarz
San Diego, CA

On The Lot one contestant shot a movie with a continuous shot that actually was really continuous. Quite amazing. I know that in the ending sequence of Music & Lyrics, they do a fade, where they kept the camera on a dolly, and you can only tell because of the slight change in lighting. They pulled it off quite well.

"We all have the potential to be great. It is our inability to do so that makes us miserable." C.S.Lewis

The 6 minute shot in Children of Men is in four different locations. Each change required a different type of effect. To do something like that yourself it can be as simple as RJ suggested - have something pass in the foreground.

I did a 26 minute shot in my movie "dark crimes". Two different shots because of the location we used. I disguised the transition with a simple whip pan. No one, even the producer has noticed. I still call it one 26 minute shot even though it's one 12 minute shot combined with a 14 minute shot.

Watch "Rope". That was shot on film so Hitchcock was restricted to 9 minute shots before the film would run out. He had do come up with interesting ways to hide the 9 cuts in the movie so it looks like one, continuos shot.

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The aim of an argument or discussion should not be victory, but progress.
Joseph Joubert, essayist (1754-1824)

certified instigator....is there any way I could see this 26 minute shot...im pretty interester in seeing it.