“The Sand Castle” is made up of intentionally simple elements: an abandoned island, a creaky old lighthouse, an intermittently working radio. And at its center is a family of four: a doting mother, a resourceful father, a moody teen son and a daydreaming daughter. Their survival depends on the increasingly Sisyphean task of waiting and scavenging, hoping and praying. Help, they hope, will soon come their way. But what at first feels like a modern-day “Robinson Crusoe” adventure soon turns into something darker and altogether more timely. While Matty Brown’s dreamy film plays more like a children’s fable than the harrowing thriller it sometimes flirts with becoming, its oblique stab at storytelling ends up muddling its ambitious vision and well-intended message.

Survival stories hinge on the grit and resilience of its characters. Food is scarce and fresh water elusive. Sleep is near impossible and shelter close to untenable.