Here is my preliminary sketch I did, but the dimensions ended up all wrong. I came up initially with about 30 inches wide/high/deep, but it actually originally ended up 24 inches, as seen below, and then resized to 20. In my first attempt I had constructed a hollow block of foam and used the harness from a hardhat with a homemade chinstrap to attach it to my head - but when put together the foam was heavy and ungainly and I could not lean too far in any direction. I don't have a photo of the materials I used for the second version, but I'll tell you: a bicycle helmet (the "round" batting-helmet style); 8 2-foot-long steel-core stakes, the kind used to support saplings and such; several lengths of plastic "corner guards"; plastic canvas; yarn; and of course duct tape. Tools needed were a hot glue gun and glue, a Dremel with large fiberglass-enforced cutting discs, a drill, and scissors.
Well, here is the 24-inch frame (I later went back and resized it to 20 inches which was a nightmare, and not necessary to describe). I'm sorry I didn't take photos during construction, but the clear plastic corner guards were so transparent, they didn't photograph well. So, what I did was, I drilled four holes into the helmet, going into it as paralell to the ground as possible, going towards the four corners of where the frame would be. The garden stakes were pushed into the holes (at their full 24 inch length) and cemeted with hot glue. The frame itself was made of the corner guards, cut into - okay let's just say they were always 20 inches - eight 20 inch pieces (four for the top square and four for the bottom); the posts on the corners were about eight inches in the back, and 6 in the front (yeah it slopes forward a bit, I found that if I didn't do that I would have to practically look at the ground all the time to keep the top of the frame level). The resulting frame was then lined up over the plant stakes, which were marked to the appropriate length and cut with the Dremel. Then the frame was cemented in place with hot glue. Now, this photo was taken before I resized it to 20 inches, and the stakes weren't as horizontal then. So imagine this whole thing smaller and lower, and that was the actual final result.
This is a closeup of how I sewed stitched-together strips of plastic canvas to the top level of the frame. I did this to round off the edges. After this I took the other four plant stakes, cut them down to about 20 (maybe more like 19, really) inches with the Dremel, and duct taped them to the edges of the frame (so that they were even with the top, and extended below the bicycle helmet). Then similar (though wider and stiffer) strips of plastic canvas were stitched around the edges of the frame, rounding those; and finally a flat strip was sewn around the bottom, open and overlapping in the back.
So, this is what it looked like then. Front view.
Back/side view. (You can see how the strip on the bottom is open in the back.)
And this is it on me. I wasn't sure before, but I think it's pretty clear now that my viewport will have to be the kid's mouth. It's probably better than it being his eyes, anyways, as they are so far apart I'd have to walk around with my head tilted to see where I'm going. But now I'm not sure where the fan is going to go.