The old postapocalyptic shuffle is alive in Young Ones, but this catastrophe is more credible than most such speculations. The problem here is water, which has evaporated, at least in this corner of the world. Patriarch Ernest Holm (Michael Shannon, apocalypse vet from Take Shelter) trades trinkets in exchange for supplies, and just manages to keep hold of his “farm”—a patch of brown desert—in hope that the soil needs only the rain to come back. But the film’s real attention is on the next generation, played by a trio of child stars aging into young adulthood. Holm’s patient son Jerome (Kodi Smit-McPhee, the kid from The Road) and resentful daughter Mary (Elle Fanning) must negotiate their future with the ambitious Flem Lever (Nicholas Hoult of Warm Bodies, soon to appear in the Mad Max reboot). Ernest isn’t crazy about Flem hanging around with Mary, for reasons that turn out to be pretty well-founded.