The ABC reported the incident occurred 4 June on a farm near Dinninup when the victim and his 11 year old friend were helping family friends.
Both children fell into a grain silo as it was being towed across a paddock late on Sunday afternoon.
The 11-year-old boy survived but the older boy died at the scene despite attempts to resuscitate him.
A spokeswoman for WorkSafe said two investigators would travel to the farm from Bunbury tomorrow to investigate the accident.
Police said a report would be prepared for the coroner.
