Los Angeles County firefighters responded to 835 Lennon Street at about 4:30 p.m. where a two-story single-family dwelling was burning.
"The child was medically treated, transported to Gardena Memorial Hospital where he has since succumbed to what we believe is smoke inhalation," said L.A. County Sherriff's Homicide Lt. Mike Rosson.
Sherriff's officials say that the child was found near a bathroom on the first floor. His mother was upstairs resting when she smelled smoke. She escaped from the burning house through a sliding door and made her way down from a second story balcony with help from another adult.
The mother is being questioned by homicide investigators.
"She's obviously very upset," said Rosson. "Very despondent, so we are treating her as best we can at this time."
Firefighters extinguished the home in less than an hour. While inside the home there was a flare up, but it took no time for them to put out the hot spots.
"I just seen the chimney on fire," said family friend Roselle King. "I just knew it was the house. I came here and the ambulance was already over here. But they were still trying to search for the little 4-year-old. Then they got him out of the house, they were trying to revive him, but he didn't make it."
Neighbors say that the mother lives at the home with her three children- the 3-year-old boy who perished, a 9-year-old son, and 20-year-old daughter.
Authorities say the daughter wasn't home at the time of the fire, but she and a male companion were driven away from the scene in the back of patrol cars.
Neighbors came together to pray for the family while investigators comb through the structure looking for clues as to the cause.
"My heart just goes out to the family and everybody," said neighbor Arnold Webb. "We are all grieving right now in our neighborhood."
Investigators say the 911 call came from a postal carrier delivering mail. The cause of the fire and point of origin is under investigation.
In earlier reports the L.A. County Fire Dept. said two children died in the fire, but later revised their information. It also was reported that the boy who perished was 4 years old instead of 3.