We had lots of fun making these. We were just playing around with cutting out paper shapes and these faces happened!
It is as simple as sitting around with some paper and scissors and suggesting cutting out face shapes. The beauty of it is that you can arrange and trim and rearrange the shapes as much as you like before you glue them down. A really great way for a child to practice self critique, because it is no problem if it does not work out, it is so easy to change. Even if they like one of their arrangements, it is still fun to try others just to see what they would be like, before you get the glue out.
To start with, just two different colors of paper are all you need. Cut out some head and face feature shapes.
Arrange them on the paper, and trim or cut new bits out, and rearrange.
When it is just right, get out some glue and glue the pieces in place.