If you are fortunate enough to live in the suburbs, allow the children to wash the auto outdoors. Be prepared to re-wash it though.
1
Give each of the children a bucket filled with water and soap solution, a cloth, and a sponge.
2
Step 1 is to hose the auto down, step 2 to wash it with the soap solution, step 3, rinse off with the hose, and finally step 4, if they get this far, dry the auto.
3
Each child gets a section to do, wetting washing rinsing and drying.
4
Whisper into one ear that so-and-so is looking hot, and maybe just a squirt of water will help.