Blow up a balloon. Spread a plastic tablecloth or sheets of newspapers on a table to keep the mess contained.
Mix white flour, a teaspoon of table salt and warm water in a large plastic mixing bowl --- a large cereal bowl works well for most small projects. The flour and water will form a paste and the salt prevents the flour from souring and growing mold. Mix the ingredients until the mixture is like oatmeal.
Tear the newspaper or scrap paper into strips or pieces. Newspaper works very well, but you can use any type of paper except for glossy inserts and pages from magazines.
Dip the paper in the paste and place the pieces on the balloon one by one. The pieces should overlap and the entire balloon should be covered in one smooth layer.
Once the balloon is totally covered, add a second layer. Add as many layers as necessary. This will give you your basic shape. When you're finished let the papier-mâché dry until hard, usually overnight.
Pop the balloon with a pin or a pair of scissors. Remove the balloon and throw it away. Now you have a hollow ball of papier-mâché.
Cut the papier-mâché ball in half. One mask can be made out of each half. Cut out two eyes and holes for the nose and mouth with scissors or a utility or X-acto knife. Put more papier-mâché layers over the cut edges to strengthen the mask. Make a slit on each side for places to thread ribbons or strings for ties, and reinforce these slits with more papier-mâché.
Use more papier-mâché mixture and more paper to sculpt and attach ears, a nose, a chin, eyebrows and hair. Be imaginative. You can add horns, a clown's nose, animal ears or whatever interests your child. Laundry lint soaked in the paste is great for sculpting all sorts of objects. Or you can use paper rolls or balled-up paper held together with masking tape to create shapes; attach them to the mask with tape and then cover them in papier-mâché.
Paint your mask with nontoxic water-based paints. Spray paint or nontoxic markers will work too, but only if you coat the entire mask with a base coat first, such as a white acrylic latex house paint. You can use regular Elmer's glue to add glitter, straw hair or other decorations.