The boy, from Wahroonga, had complained of a sore stomach on Wednesday night and couldn't eat much dinner, The North Shore Times first reported.
After he woke from pain a few times during the night, his parents took him to Hornsby Ku-ring-gai Hospital early on Thursday morning.
After a few hours, the boy was reportedly feeling a bit better and his was sent home at 7am, with hospital staff reportedly telling his parents to keep an eye on him, SMH reports.
But very quickly, his condition worsened and his parents rushed him to Sydney Adventist Hospital at 2.15pm. Heartbreakingly, the child died two hours later.
A coroner is now investigating the case.
This article originally appeared on marie claire.