Such is the world of Alfonso Cuarón’s “Children of Men,” a 2006 film with shocking parallels to reality. Unfortunately, compared to other works in the post-apocalyptic genre, “Children of Men” didn’t perform particularly well at the box office. “Children of Men” suggests the opposite, highlighting a way in which a declining population may lock us into a downward spiral rather than some new managed path. Finally, despite its grim setting and framing, “Children of Men” is also a movie about optimism and human persistence. Alfonso Cuarón lays out a world that is eerily similar to our own in ways far too close for comfort.