The wreck happened around 12:30 on FM 973 near State Highway 130 and the whole thing could have been caused by a cigarette.
Department of Public Safety troopers said an Oldsmobile was headed north on FM 973 when the driver crossed over the roadway and hit an oncoming Chevy SUV.
A teenage passenger in the Oldsmobile told troopers his mother was driving the car and ashes from her cigarette landed on her lap. According to the teen as the woman tried to remove the ashes from her lap, her car drifted across the double yellow lines. By the time the driver looked up it was too late and she hit the Chevy SUV head on. After the crash, the Chevy caught fire and by the time first responders arrived the car was engulfed in flames.
Austin Travis County EMS said six people were injured during the wreck. Four children were transported to Dell Children's Medical Center. A spokesperson for EMS said one child is in critical condition and the other three suffered serious injuries.
A 30 year old female and a 20 year old male were taken to University Medical Center Brackenridge and are expected to survive.
DPS is investigating the crash.