HALTOM CITY -- Looking at the stuffed animals, flowers and candles that had been left as a memorial at her home, a grieving Yessenia Garces desperately searched for answers."I don't know anything that is going on right now," Garces said Friday, the day after a house fire killed her two children, mother and nephew. "I want to know as much as anyone wants to know. I want to know what happened to my babies. I want to know what happened to my mom."Pressing her hands against the sides of her head, Garces spoke tearfully about her losses."I have to do four funerals," the 23-year-old mother said, crying. "I just didn't expect to come home to this."Garces was at work when the fire broke out Thursday evening, killing Maritza Garces, 52; Gene Perrera, 5; Jayleen Rayos, 3; and Jaime Moran Jr., 2 months.Gene and Jayleen were the children of Garces; Jaime was her sister's son.Investigators traced the fire's origin to a spot near a Christmas tree in the living room. But on Friday, they still didn't know what started the blaze.Haltom City Emergency Management Coordinator Perry Bynum said an arson task force would continue investigating.Bynum called the fire among the worst he could recall during his 24-year career."It's the type of fire that is very difficult," he said. "Not just for the firefighters but for the community, too."'They're just like my mom'Outside the home Friday morning, neighbors had left stuffed animals circling a tree in the front yard. An inflatable snowman was crumpled on the lawn. Inside a broken upstairs window, an infant carrier and car seat could be seen.Garces said she appreciated the mementos left by neighbors."My kids were raised on this block," she said. "Everyone knew them. They were the most kind-hearted kids in the world. Everybody fell in love with them."She said the children got their good nature from their grandmother."They're just like mom," she said. "They took after my mom."Delario Kizzee, the owner of the Haltom City house, said the grandmother started renting the house in 2008."She was a good woman," Kizzee said.Fire alarms blaringThe fire was reported at 5:02 p.m. Thursday in a call from the 4900 block of Colonial Park Drive, said Haltom City Fire Chief Steve Ross.Smoke detectors were blaring when firefighters entered the home, Bynum said.The woman, he added, was found on the ground floor and all the children were upstairs.Investigators on Friday did not know why the family was unable to escape."In this case, there's nothing that we can see that's obvious about why they couldn't get out," Bynum said.When ambulances arrived, firefighters had pulled two victims into the front yard and two more were pulled out not long afterward, said Matt Zavadsky, a spokesman for MedStar.The children were transported to Cook Children's Medical Center in Fort Worth and the woman was taken to North Hills Hospital in North Richland Hills, where they were pronounced dead.'It's devastating'Thursday night, neighbors remembered the little boy, who was frequently outside looking for other kids to play with him.Phillip Heard, who lives with his family across the street, said that when he was out working in his garage, the boy would walk up and ask him what he was doing.Heard said he was outside about 5 p.m. Thursday when he saw smoke billowing from a downstairs window of the house. No cars were parked out front, and there was no other indication of whether anyone was there.He said he yelled, "Your house is on fire! Hey! Is anyone in there?"Getting no response, he called 911."It's devastating," Heard said. "I can't believe it happened. I just feel bad I couldn't help."Eight companies responded, including units from Haltom City, Fort Worth, North Richland Hills and Watauga, Ross said.The first unit reported smoke coming from the second floor."The fire was put out quickly, and they did a thorough, rapid search," Ross said.Staff writers and Deanna Boyd and Bill Miller contributed to this report.