YOU are your child's best instructor, and starting as early as they'll pay attention makes a big difference in their ultimate road safety, courtesy, and insurance cost.
One absolutely monumentally huge problem with drivers in many parts of Texas, and I have to say Houston is BY FAR the worst of anywhere in the world I have driven, is how discourteous and thoughtless drivers are. Simple things.... like cutting someone off at the last moment to take your exit... waiting until the last possible moment to merge two lanes into one -- while pacing the car next to you to prevent them from merging... like driving whatever speed YOU want to drive, in the left lane, while the 5 cars behind you want to get on down the road... like driving right next to another car on a two lane road, effectively forming a roadblock and also putting you BOTH at a disadvantage should something require evasive action (a kid runs into the roadway, would you rather quickly slide over a lane or run over the child? Houstonians seem to prefer the latter). I could go ON and ON and ON about how utterly bad drivers in Houston are.
You can drive for 2 minutes and see someone do something stupid here. Most of the time it doesn't even take that long.
To get back to the point, the more you teach your kids about driving BEFORE they're behind the wheel, the better prepared they are for when things go wrong. Things WILL go wrong, but you can be ready for them. A VERY large percentage of accidents are avoidable, by compensating for the SINGLE reason they happen in the first place -- not paying attention. If every driver was paying attention 100% of the time they were behind the wheel, the accident count would drop to nearly zero. Teaching kids to keep their eyes, ears, and MIND on driving, you'll keep them alive, uninjured, and keep the car smash-free.
Teach your kids to anticipate. Make sure you teach them how to build a mental "map" of everything around them - where the road is going, how the lanes are changing, where their next turn/exit is, how fast and how long until they need to make the next course alteration, where every car around them is and what you think they might do next. Teach them how to handle the car when things go awry - I wish EVERY driver had some basic emergency driving instruction, to be honest. How to handle the car if/when you hydroplane in the rain. How to handle the car if/when you skid around a turn because you entered it too fast. How to handle the car if something fails - brakes, steering, you drive a Toyota and the throttle sticks

All of these things are manageable, but there's no actual driver training in the US unless you seek it and pay for it yourself. Sign on the line, here's your license.
Lastly, teach your kids to be courteous! Traffic flows FASTER and smoother, when drivers work WITH each other. Think about trying to get out of a burning sports arena - you're trapped inside with the fire lapping at your heels, while the people who just stepped through the door are now standing around BLOCKING the door because "well I'm safe now, I'm good." Think about others on the road, and do unto others as you'd have them do unto you. You'll get where you're going faster, with less stress, and even better gas mileage.
