The summary goes something like this. A family with a young child is about to enter the last ship departing earth. They're told they cannot carry their pet dog along. Aghast, they leave it behind. The young kid does not understand the reason for the evacuation (which I vaguely remember as a global nuclear fallout). He sneaks out to rejoin with the pup. The parents caught in the commotion, realize only after the ship has departed that their kid is missing.
I'm finding it hard to trace where I read this story, but, I recall writing an essay on this. If it helps, I suspect it was a part of my school curriculum here in India around 2000-2005.
Could anybody please identify/trace this story?