Thank you, once again, for your comments.
Since I see people seem to be liking this thread I'm sure no one will object if I post some more photos.
In my initial post I mentioned that we first made a "Gibson" from a piece of scrap plywood and an old floor beam, from a dumpster. Here's a picture of that guitar.
The "frets" are just drawn with a marker and the "pickups" are empty Altoid's boxes. Somewhere along the way I mentioned that we couldn't make a real Gibson but my kid (at the time 5 y/old) insisted that it had to be a real Gibson, so, I wrote "Gibson" on the headstock and that ended the debate about the authenticity of this guitar. However, I do have to mention that an expert eye could probably spot right away that this Gibson is not authentic.
Anyway... at that point I thought that was that. But for the next few weeks he wouldn't put the guitar down and I was looking at my kid strumming and strumming at a plank of wood with 6 strings, of which one might have even stayed in tune. At some point I thought he earned an upgrade. So, at this point two things happened. We started building another one and we also upgraded this prototype and made it into a real playable instrument, with real frets.
The story of how it all started is a bit humorous.
My kid had been spinning old 45's for about a year and a half. One of his favorites was Chuck Berry. So, one day I decided to show him Chuck Berry on YouTube.
First question: "Papa! What kid of guitar is that?"
"That's a Gibson ES-335." (I believe it was actually a 355, but whatever...)
"I want a Gibson ES-335."
"OK, when you grow up, you'll be able to save some money and buy one."
"I want a Gibson ES-335 now."
"Now you can't, 'cause you're too little."
"I'm not too little..."
"I want a Gibson ES-335."
"When can I have a Gibson ES-335?"
"Why can't I have a Gibson ES-335?"
You get the picture.
He kept watching the videos and asking me what each part of the Gibson ES-335 was called.
Then he started drawing pictures of the Gibson ES-335 and telling me all the details of what it had to look like and that it had to have: two f-holes, this headstock shape, two cutaways, two pickups, a pickguard, six strings, six tuners, and so on... And each time, "When can I have a Gibson ES-335?"
I have a stack of drawings that he made. I believe this was the first one.
His drawings gave me the idea to make a Gibson ES-335 at home. What I had in mind, at that time, was a toy. So, I told him he had good (and expensive) taste in guitars and asked him if we should make one.
He was so happy and enthusiastic that it immediately became clear that this was the point of no return. We had to go and make a Gibson ES-335, right now.
I believe it took me about an hour to print a sized-down outline, trace it on a piece of scrap plywood, cut around with a jigsaw and make a neck from an old floor beam. I installed two large wood screws for the strap and hang the guitar around his neck.
"Where are the tuners?" was the question.
So, I mounted six wood screws on the headstock to make it look like tuners.
"Where are the strings?" was the next question.
At first I tried to talk him out of this idea and said it was impossible to put strings on this guitar. But my kid never gives up, so I had to figure out how to put strings on it.
I had a extra bridge and six tuners, laying around, from an old guitar. So, I removed the six faux tuners, mounted real ones, installed a bridge, put strings on and tuned the plank of wood to open G. The neck was so flexible you didn't need a whammy bar.
Here you can see the holes at the side of the headstock, where the faux tuners used to be.
At first I didn't think I was going to put any strings on, so later I had to figure out how to raise the bridge. Here's a view.
The action was really high, the neck got a bit bent, but he just kept strumming, at first using a slide and eventually without one. He even had to take the guitar to bed a few times. It became his favorite thing.
I don't have a habit of posting photos of my kid, online, but here's one where you can't see his face.
I took many more photos of the build and since this thread now has some readers I'll post more at some future time.