Toys made of paper. Some are based on the Origami craft, others are more complex and have moving parts.
There are even some projects for papercraft automata. Good for all ages!
Here you have a good selectiong of ready to print and fold papercraft templates. They are in PDF format, most seem to fit on a single page. There aren't much description but I don't think you need anyway.
How To Make Paper Craft Model From Scratch
Click here to view the instructable
This site has a large number of guides for papercraft toys. Most are good for little kids.
How to Create Your Own Custom Papercraft Toy
This site publishes plenty of papercraft patterns and links. Not all of them are good but the content is frequently updated.
Animated Mechanical and Optical Illusion Paper Toys
Rich collection of papercraft toys. Optical illusion toys, automata, cams and cranks - all made (mostly) of paper.
See the instructable.