The Los Angeles County medical examiner confirmed Cameron Flores died from fentanyl toxicity. His death was ruled an accident.
The toddler was found unresponsive at Melville J. Courson Park on May 22 and rushed to Antelope Valley Medical Center, where he later died.
The boy's father, Schaffer Grindstaff, 29, told deputies his son was suffering from a medical emergency. Grindstaff and the boy's mother, Amanda Flores, 30, were each arrested and released days later.
Online records indicated the reason for their release was insufficient grounds for making a criminal complaint.