Safety Note: Dremel(r) tools and accessories are not intended for use by children under the age of 18. Check and secure sanding band accessories before each use. Maximum operating speed is 35,000 rpm.

Once again, the goal is for the kids to build the cars and have fun (see the topic "Derby is For Kids"), so making a mess isn't bad, as long as it's safe.  Kids are best at the design, hand sanding, painting and decal portions.  Heavy cutting should be done by adults, but make sure the Cub has done at least 50% of the overall effort.

The Derby website has a game which lets the kids print a design for tracing. Or just trace the block on to the paper and have the Cub draw his design within the outline of the block. 

The adult can then cut it out with a coping, scroll or band saw and maybe do some rough rounding with the Dremel.  Have the Cub hand sand the car and then maybe work with the adult to add some carved details such as grill work, etc.

Leave the painting and finishing stuff to the Cub.

Remember the winner isn't the Cub who's car makes it down the track fastest, but the one who has fun, learns something and sticks in Scouting, so that the Scout Oath and Law stay with him throughout his adult life.

Yours in Scouting,

Gary