The driver "lost control and left the runway, crashing into parked vehicles and striking spectators who were observing the races," Kerrville police said.

A 6-year-old boy and an 8-year-old boy were killed in the crash Saturday afternoon at an event called "Airport Race Wars 2" at the Kerrville-Kerr County Airport, police said in a news release. The organized event was attended by thousands and involved drivers speeding down a runway as they competed for cash.

Authorities have not released the identities of the two children who were killed at the event about 60 miles northwest of San Antonio. Members of the Kerrville Police are investigating the accident.

The race was an eighth of a mile (0.2 kilometers) long, and water-filled plastic barriers lined the course. But Amestoy said they didn’t extend past the finish line, leaving no protection between spectators and cars as they were slowing down at the end of the race.

Spectators could get within about 15 feet (4.6 meters) of the track, and many watched the race from lawn chairs in the absence of stands. Organizers reminded people to stay in the grass and off the asphalt,  Amestoy told The Associated Press in a phone interview.

The driver was nearing the end of the strip when the car veered off course, Amestoy said.

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The Kerrville Convention and Visitors Bureau’s website promoted the event as an "action packed, family-friendly day" in which fans could watch the "fastest drag cars compete for over $8000 in total prizes."

Fox News's Emma Colton contributed to this report.