What is the theme of the story "The Sandbox" by Edward Albee?

Edward Albee was a particularly cynical observer of American society and the unrequited pursuit of the mythical “American Dream,” a theme he would explore more directly and at greater length ("The Sandbox" is a very short one-act play) in his 1961 script titled, appropriately enough, The American Dream.  Albee’s plays invariably adopt a harsh tone towards the cliché of a better life and the hypocrisies that permeate much of humanity.  "The Sandbox," as noted, is a one-act play, intended to last about 15 minutes.  It has five characters: Mommy, a tyrannical, sadistic middle-aged woman; Daddy, her put-upon emotionally weaker husband; Grandma, an “86-year-old woman with bright eyes” who presents to her caretakers, Mommy and Daddy, the persona of the childish, feeble elder but who conceals (and reveals only to the audience) an astute active mind; the “Young Man, 25, a good-looking, well-built boy in a bathing suit”; and The Musician, whose musical accompaniment is used for satirical purposes.  Mommy and Daddy have brought Grandma to the beach for the day and dutifully deposit her in a sandbox where she will presumably be safe and contained.  It becomes rapidly apparent that they have little regard for Grandma and are simply and nonchalantly awaiting the old woman’s imminent death.  Grandma, however, is fully cognizant of her family’s disregard for her continued well-being, so it is with no small amount of irony – irony grounded in the aforementioned hypocrisy that is at the center of much of the playwright’s work – that Mommy and Daddy feign genuine concern for Grandma when they think she is finally about to expire:

Mommy (barely able to talk): It means the time has come for poor Grandma … and I can’t bear it!

Daddy:  I…I suppose you’ve got to be brave.

Grandma, however, is not quite ready to go into that good night.  She continues to act the rambunctious child while communicating directly to the audience her awareness that she knows exactly what she’s doing and will go when she’s damn well ready.  She does, of course, finally succumb, and it is now that the handsome, muscular young man exercising continuously nearby reveals himself as “the Angel of Death,” come for Grandma. 

Albee’s portrait of an uncaring, hypocritical middle-aged couple presages the characters of George and Martha in the playwright’s landmark work Who’s Afraid of Virginia Woolf, which would be published soon after "The Sandbox" and The American Dream, and would form a sort of trilogy of despondency regarding that elusive dream.  As we get older, Albee seems to be saying, we become increasingly irrelevant and increasingly more jaded regarding our lives and those of others.  At the end of the day, we all just die and go away.