In The Children of Men, childbirth has suddenly stopped; there are no more children being born and society is beginning to collapse as people believe that there is no future and no reason to continue living. One effect is mass suicides, described as a process called Quietus:
...Jasper said, "You've heard of the Quietus, I suppose, the mass-suicide of the old? ...there are people who like to make an occasion of these rites of passage. It's happening in one form or another all over the world. I suppose there's comfort in numbers, in ceremony."
(James, The Children of Men, Google Books)
Because there is no future for the human race, and because people feel they have little-to-no reason to continue living, the elderly are committing suicide as a ceremony, covered without judgement by news organizations. It turns out that many of the old people participating are drugged by the State, which is encouraging the Quietus to keep their economy viable; elderly people use up resources that the younger desire, and overall production is down because of the general malaise. Some citizens try to fight against the State-sponsored Quietus because they believe it is only a ploy to keep people under control, and because they do not believe that every person participating is doing so of their own free will.