The blaze broke out just before 2:30 a.m. at a home in the 8500 block of Cliffdale Road.
Police said a passer-by reported the fire after seeing flames near the back of the house. By the time fire crews arrived at the scene, flames were shooting through the roof.
Rescuers found 25-year-old Ashley Bullock and her two boys, Trayvon and Andrew, ages 5 and 6, dead in the same room inside the home, according to authorities.
"It's a firefighter's worst nightmare," Fire Battalion Chief Ron Lewis said. "Obviously very devastating for this young family and just heartbreaking for the whole fire department.
Ashley's husband, Juaan Bullock, was working the night shift out of town when the fire started.
"They were just good fun, cool people," family friend Martin Kearse said. "They were good. She would babysit for me if I needed her to ... she was going to school and everything."
It took crews about 45 minutes to get the blaze under control.
Fire crews didn't hear an audible ... smoke detector when they entered, but I have talked to ... the gentleman that lives here and there were working smoke detectors in the house at the time," Lewis said.
Officials have not said what caused the fire. Detectives are still investigating the incident.