Paperfoldables.com is a great site where you can print free PDF templates for 3D paper models, both paper animals and paper people. Just print, cut, fold and tape. These crafts might be a bit hard for your preschooler, but if you build them together they can certainly have fun playing with the finished designer toys!
If you like these, you might want to buy the book Urban Paper: 25 Designer Toys to Cut Out and Build