Paper models are most complicated crafts on the DLTK websites, but they are fairly simple examples of paper models in general. They provide a good introduction to the fun and time consuming hobby of paper modeling and are suitable for children ages 10+ for the most part.
The 3D hanging versions are the simplest types and are suitable for ages 5+.
3D Hanging Crafts (Age 4+)
3D Pop Up Cards (instructions)
Also check out 3D Geometry Nets from Kidzone.ws