They aren't very good about advertising it on their websites (either TMS or Speedway Childrens Charities).
Basically, they send e-mails out to the local DFW car clubs and mention it on TV the day of the event. If you have a car club of 12 cars or more and you want to run together, you need to make reservations for a time slot. If you don't care who you run with, you just show up and they will fit you in.
They line you up in the pits and you follow a pace car, but depending on the group you are running with, speeds range from 65 mph to 85 mph (+ for short bursts).
Kids 6 and over are allowed in the car, car must be licensed and registered.