My first thought was something wearable but since he is only 2 and I didn't want it to be lame and dangerous, I decided on something he could ride in. At the moment we have a whole selection of stroller so that seemed like a perfect frame and it saves it from having to be durable enough to roll and turn.
Now i've got an idea, a kid, a frame and I can really get started.
Step 1: Planning
Everybody knows what a bobcat looks like right? I could have just free-handed something and started cutting but I didn't want to waste time (the time for building this came mostly out of sleeping time with 2 kids in the house) and material so I started looking in Sketchup's 3d Warehouse at the existing models until I hit upon one I liked, the Carepillar Skid Steer 236b. (http://sketchup.google.com/3dwarehouse/details?mid=ef2791b1894dd31478fe949fc1419876)
This model is much more detailed than I would like and I need to simplify it before I can make my templates. I exported a 2 cad drawing from Sketchup ( I have a Pro license at work, if you can't export as a .dwg it is easy enough to export a .jpg and trace it.)
After tracing the exported image and simplifying it along the way, I drew a 4x8 box and planned my cuts to be as efficient as possible.
If you have access to a large format printer run off a print of what you've drawn and go to town. I was able to piece them together from 11x17 and print it on scrap. A little taping and I was ready to go.
Below are the model and the CAD drawing.