You won't get much more simple that this crayon hauler but you will end up with a project the child can enjoy. You will probably need to cut the body but the child can help assemble the wheels, paint and decorate as they like. Maybe even help drill all the holes for the crayons.
The truck is designed to be cut from a construction grade 2 x 4. The wheels are 1 1/4" diameter and can be cut from the pattern or purchased. You can buy the wheels from many craft and woodworking stores. I included a link to where you can buy them online.
I kept the truck in the picture above very simple but you can add fenders, head lights, spare tire, caution light, smoke stacks and anything else you or your youngster can think up. Remember to keep the age of the child in mind when adding parts that could come off and be swallowed.