Built a treehouse with my 6 year old and it actually didn't fall down

Spent all last Saturday in the backyard with my son nailing together a treehouse. I had zero confidence this would work but watched a bunch of YouTube videos and just went for it. Used mostly scrap wood from the garage and some 2x4s I had lying around. The thing is actually sturdy and my kid has barely left it. Best $40 I spent on hardware. Now my 4 year old wants one too so... I guess I'm building another one next month.