I think for a strong house you would need to use solid wood pieces - eg kiln dried pine cut to size for the sides, back etc. Kiln dried solid pine is fine - it is the pine shavings that are the problem as they have a lot of shaved surface area. As long as the pine wood that is cut to size is untreated and kiln dried it would be safe.
Like this kind of thing. Even with solid wood there can be splintery edges etc so sandpaper is your friend
I get a medium grade and a fine grade sheet. The medium grade is general for rough bits. The fine grade is brilliant and sands edges absolutely smooth. Only takes a few minutes
https://www.amazon.com/Kiln-Dried-Pi...ateway&sr=8-62