Burleson police say a 4-year-old boy started a minivan and then ran over his mother and brother, killing the 3-week-old infant.
The crash appears to be a freak accident, police said.
Chassey Bates and her three young sons were visiting their grandmother at the Mockingbird Hill RV Park on South Burleson Boulevard.
Police said Bates' 4-year-old son somehow got in the driver's seat. His brother was beside him in the passenger seat. The 4-year-old put the keys in the ignition, pulled out of park and the van began moving, investigators said.
Bates, who was holding her 3-week-old son Chase, ran out of the RV and tried to stop the vehicle. She and the infant were hit and run over, police said.
The van eventually hit an RV hookup.
"We were in the RV, and we heard a lot of screaming, and we looked out the window, and we saw that the van had, at that time, had stopped rolling," neighbor Craig Lessard said.
One man turned off the van while the children got out, police said. Lessard ran out of his RV and found Bates under the van. He and a few other men lifted the van off of her.
"Then I saw her take a breath when I took the weight of the car off. At that time, I told another gentleman to drag her out," Lessard said.
"She just was crying out in pain, wanting to see her child. She just kept asking about her child," said Bonnie Wooley, the RV park manager and a neighbor.
The infant died at the scene, police said.
Neighbors said his brothers were crying.
Bates' husband was not at the RV park during the incident.
Bates was in the hospital Friday in serious condition. Neighbors said she sustained broken bones and a punctured lung.