The end pieces were the most challenging part of the project. First I drew their shape on the computer using OmniGraffle, a 2D drawing program for the Mac. Using a 1:1 scale printout as a pattern, I cut it out of 1/4" plywood using a scrollsaw, and fine-tuned it with some sanding. Then I rough-cut the end pieces out of walnut using a bandsaw. The plywood template was attached to each piece and followed with a flush-trim router bit to copy the pattern exactly to the walnut. In this way I was able to produce two identical end pieces.
1/2" oak dowels form the eight cage bars. The balls were purchased from Woodcraft. I think they are made of maple.
The majority of the holes don't go through the wood and have flat bottoms. They were done using forstner bits on a drill press.
To make it friendly for small fingers, all edges were rounded by a 1/4" roundover bit in the router. Each part was sanded with 150 and 220 grit sandpaper, and finished with two coats of Minwax Tung Oil Finish (actually an oil/varnish blend). The balls were painted with several coats of Testors oil-based enamel paint, the kind sold for painting plastic models.
Other than a small hardwood dowel for attaching the handle to the frame, no fasteners were used in this piece. Only glue and joinery. Dadoes were cut on the table saw because I was having chip-out problems when trying to do them with the router.
The final toy is about 28" long, and 14" wide. The wheels are 6" in diameter. This design is my own, but I roughly copied various popcorn mowers I saw for sale on the web.