I built Joseph a bunkbed for his 4th(!) birthday. I don’t have much for gratuitous making-of photos, but here are a few of the finished product. Let me know if you’re interested in more detailed pictures (up close, joints, connections, that kind of thing).
The wood is top choice white pine, which you can find at your local Lowes/Home Depot.
I knew staining it would be a bad idea as Joseph would likely end up denting and marring it (he’s rough, and pine is soft), so I kept it the natural look, which I like quite a bit. And to help protect against fingerprints and such, I used this Minwax water-based Poly.