The event, Airport Race Wars 2, was taking place at the Kerrville-Kerr County Airport, around 70 miles from San Antonio.
Police said the vehicle lost control and before crashing into parked vehicles and striking spectators.
“The race is shut down, ” he said. “We ask that you please pray for everybody involved.”
Four of the injured adults were taken to a hospital by air ambulance. Two adults were listed in critical condition at University Medical Center in San Antonio, police said.
The youngest victims, a 4-year-old boy and a 3-month-old girl, were transported to Peterson Regional Medical Center in Kerrville by ambulance for precautionary evaluations, according to police.
“Kerrville Police are conducting an investigation into the accident,” the police department said. “This investigation is active and ongoing.”
CNN’s Jennifer Feldman contributed to this report.