Supervised Scrubbing

I like to keep my cars clean, even though I don't always keep up as well as I should, and the kids always want to help me. I'm weird about washing cars though, and it always makes me nervous when they start attacking the cars with anything. I'm always worried that they'll drop the sponge in the dirt and pick it back up and just start scrubbing. With dirt from our dirt driveway stuck to the sponge, that would be pretty close to rubbing the car with sandpaper. It freaks me out and I spend more time watching them and worrying about what they're up to than I do washing myself. It's pretty stressful.
I've finally figured out a compromise that lets them scrub to their hearts content, and lets me not worry about them. They get to wash the wheels and the tires, and I get to wash the rest of the car. They have to start with the shiny parts, the wheels, and then move to the black parts, the tires. They can understand that and they do a good job. They have their own sponge and brush for their jobs and by the time they're done with all four they're pretty bored with the work and are ready to move on to some other adventure. This has made car washing so much more relaxing for me. I can focus on doing a good job and I don't have to worry that they're abrasively scrubbing hundreds of dollars of paint off the other side of the car.
Teaching my kids how to do jobs around the house is one of those really trying parts of being a dad. There are very few things that I can't do quicker and better by myself. I keep having to remind myself that much of what I have them do is really a benefit for them, not for me.