It was important to me to do it as a joint project. My younger son actually did more than my older son, since my younger son is currently obsessed with tools. He helped pull the trigger on the clamped drill to polish the axles with me, and also with the limited wheel prep. My older son helped with the coping saw cutting.
What was hilarious for all involved, was calling each of the scouts up at the end of the night to pick up their cars and receive a patch, and one of the poor scouts didn't know which car was his. So, the den leader asked him, "Do any of these look familiar to you?"
A good laugh was had by all.