The gunman fled the scene and police say they say they are looking for a man aged between 18 and 20 who may be armed in connection with the incident.
The man police are hunting has a thin build, and was last seen wearing grey tracksuit pants, a navy blue hooded jacket and white joggers. It's believed he may be armed, and police warn he should not be approached.
Emergency services were called to a home on Moresby Avenue at about 6.10am and found a teenage boy with a gunshot wound to his head.
It is believed Brayden's mother confronted the attacker but locked herself in a bedroom when a pistol was brandished.
Detective Chief Inspector Mark Brett said it appeared to be a targeted attack.
His mother, stepfather and two young siblings were not injured but his mother was "extremely distressed," he said.
Talking to reporters today, Inspector Paul Kremer from Macquarie Fields police said the attacker went upstairs and "forced entry to the victim's room".
It is believed the boy was shot while still in bed asleep.
"At this stage the young person is extremely critical," Insp Kremer told media.
A one-year-old baby and a seven-year-old were also at home at the time.
Insp Kremer said it was "too early to say he knew" the shooter and it was linked to an earlier homicide, although the incident has been described as a "revenge attack".
The 15-year-old was treated at the scene by ambulance paramedics before being taken to Westmead Hospital where he died.
