Preschool and early elementary
Fill one bucket or bowl with soapy, sudsy water, and a second container with clean water. Rustle up an old toothbrush, a watering can, and a spray bottle filled with water.
Ask your kids, “How should we set up our car wash assembly line? What order makes the most sense?”
Maybe they each want a specific job, like a real assembly line, or maybe they each want to shepherd a vehicle through the whole procedure.
The kids can drive each vehicle into the parking lot (which can be a dish towel), and then go through the steps (soaping up, getting rinsed, getting their windshields sprayed, getting polished, going to dry in the sun…).
This is a good activity to do on the front step, or, alternately, on the bathroom or kitchen floor. You can also contain it by having them work in the bathtub.
If you want to add a step, give them watercolors and brushes first to get the cars good and dirty.
For added fun, have the kids change into their swimsuits first.