My understanding is that the PWD is supposed to be a parent and child working together effort.
For my son's cars ...
He chose the shape and design and draws in on the block
We use the pack's pinewood debry cutting event, most years and adult would cut to the lines and/or use the belt sander. His Webelos year, he did some of the cutting and most of the sanding.
I operated the tools to cut into what remained of the car for adding weight
He did the painting, although I did help put down tape so the paint went where he wanted it.
We both sanded the axle nails to remove the barbs
I usually applied the graphite (I didn't want that stuff all over my house)
I held the axle nail and wheel spacer while he hammered it in.
He never won his den, but he did have some stiff competition.