BURLESON -- A woman was severely injured and the baby she was holding was killed Thursday evening when they were struck by a minivan that the woman's 4-year-old son started and put in gear, police reported.The first 911 call came at 7:01 p.m. from a mobile-home park in the 1900 block of South Burleson Boulevard.The woman and her children lived in the park but were visiting relatives at the time, police said.The 4-year-old was in the driver's seat of the 2005 Chrysler Town & Country minivan with his 5-year-old brother, police said.The mother heard the vehicle start and ran toward it with her baby in her arms.The van knocked them down and rolled over them, police and a witness said.The baby, identified as Chase Bates, born Sept. 4, was pronounced dead at the scene, according to the Tarrant County medical examiner's office.The mother, who had not been identified late Friday, was flown to a Fort Worth hospital by helicopter ambulance, police said.On Friday evening, Craig Lessard, 49, said he and other neighbors ran to help.One man braked the van and helped with the two boys inside, another grabbed the baby and Lessard, and two other men pulled the van off the mother, Lessard said."It was a knee-jerk reaction," he said. "We were helping someone who was in trouble. We don't even know the woman's name. They were someone that we waved hello to when we saw them."We just really hope the woman can pull through OK."The investigation is continuing, police said.Staff writers Bill Miller and Mitch Mitchell contributed to this report, which includes material from The Associated Press.