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HOUSTON (AP) _ A boy playing with a fireplace lighter ignited a blaze that killed a mother and three children who became trapped by burglar bars that blocked a bedroom window, a fire department spokesman said.

The victims died of apparent smoke inhalation when fire broke out in the single-story home Wednesday, said Robert Lopez of the Harris County medical examiner's office.

Witnesses said Stephanie Hadnot, 30, initially escaped with her mother, stepfather, two of her children and a boy staying with the family. But she ran back into the house when she realized three of her children were still inside, said her father, David Hadnot.

All four were found near a window in a back bedroom, the children in a closet and their mother just outside the closet, said Capt. Jack Williams, a Houston Fire Department district chief. He said the window was blocked by bars.

``Burglar bars played a definite part in this,'' Williams said. ``They do a good job at keeping people out of the house. And they do a real good job at keeping people in during a fire like this.''

Williams said a neighborhood boy staying with the family started the fire and could face charges. One relative said fireworks inside the house may have been set off.

The mother of the boy who allegedly started the fire said Stephanie Hadnot's mother, Sophie Hadnot, had agreed to look after him while she was at work. Sophie Hadnot told neighbors the boy was about 12.

Neighbor Reggie Allen, 21, said he saw the fire and tried to wake the people inside. ``I beat on the windows, but the bars were locked,'' Allen said.

``Nobody could get to them,'' said Lisa Shotwell, another neighbor.

Lopez identified the victims as Stephanie Hadnot; Mounique Shanta Hadnot, 16; Frank Glen Thomas, 13; and Kym Stephane Hadnot, 4.