Built a treehouse with my 6yo and it's actually not terrible
Started this project thinking it would be a disaster but my son was so excited. We used 2x8s for the main platform, bolted into the oak tree with lag bolts. Took us most of Saturday and Sunday morning. He helped drill holes and hand me tools. It's about 8 feet up, has railings, and honestly looks kinda legit. My wife was nervous at first but saw how much he loved working on it with me. Def recommend if you got the time and a decent tree. Just take your time with the bolts and don't cheap out on hardware.
Dude this is awesome. Building stuff with your kids hits different. I did a treehouse with mine a couple years back and he still talks about it. The 2x8s are solid, way better than trying to cheap out on materials.