He died, shortly before the first mission to Abydoswhen he accidentally shot himself with his father's model gun. Judging from his appearance, he was about eight years old at time of his death.
Jack O'Neill blamed himself for what had happened to his son and came close to committing suicide. However, his adventure on Abydos with Dr. Daniel Jackson brought him out of his depression and caused him to lighten up a little. Stargate Nevertheless, Sara divorced her husband shortly after his return from the first Stargate mission.
About a year later, inan alien entity, impersonating O'Neilltried to find Charlie so he could make him "better," but didn't realize how lexxi lockhart physical death was to Humans.
Charlie O'Neill -
However, the being did impersonate Charlie as Jack took him back to his planet to give him a chance to say goodbye to his son. Inwhen torturing O'Neill for information on NetuApophis used the memory of Charlie's death. Inwhen dealing with Malakaian alien archaeologist trying to make an Ancient time machine work so that he could go back and see his wife again after her death of a congenital heart condition, O'Neill used Charlie's death to show Malakai that he knew the other man's pain and convince him that the pain he would feel from reliving his wife's death wasn't worth the chance of seeing her again.
After invading Jack's subconsciousness mind inthe Human-form Replicator First made him relive Charlie's death. First told Jack that he was right to blame himself and that Charlie would still be alive if not for his carelessness.
Charlie O'Neill named President of Old Crescent as McGovern is given life membership
Ineight years after Charlie's death, O'Neill still kept a photograph of Charlie in his locker. Charlie becoming the commanding officer of Stargate Command inJack kept a photograph of himself and Charlie playing baseball in his office.
It is possible that Charlie would have had the ATA-genelike his father.