Authorities say Aydin Brown was found unresponsive inside a home on Weequahic Avenue in Newark on Monday. He was rushed to Beth Israel Hospital where he was pronounced dead.
Police initially said they were searching for his mother's boyfriend, and on Tuesday, they announced they made an arrest in the case.
Mark Harper, 36, was arrested on a charge of endangering the welfare of a child. Harper has been identified as the boyfriend of the victim's mother and was said to be caring for Brown at the time of his death.
The incident remains under investigation to determine the circumstances surrounding Brown's death.
Brown's family members described him as bubbly and full of life. He was a 2nd-grade student at University Charter School in Newark.
"Aydin was a healthy young man, Aydin was a good little boy," the victim's great aunt, Judy Ingram, said. "You take a life, your's is going to be taken too. He didn't have to do my great nephew like that. So he will be punished."
The Medical Examiner will determine the cause of death.
Newark Police Director Anthony Ambrose is urging anyone with information about any criminal or suspicious activity to call the Department's 24-hour Crime Stopper tip line at 1-877-NWK-TIPS (1-877-695-8477) or 1-877-NWK-GUNS (1-877-695-4867).