Your kids will have a blast with this technique. First you press on Con-Tact paper shapes, next you spritz paint all over the shirt, then you rip off the stencils to reveal the finished design.
Wrap the plastic bag around the cardboard and slip it inside the shirt and then lay the shirt face up on the newspaper. Have your child draw various shapes, such as the shark, swirl, zigzag, or flower shown here, on the Con-Tact paper. Cut out the shapes and stick them onto the shirt so that they are firmly attached.
In the spray bottle, mix three parts fabric paint to two parts warm water and shake. Now your child can spray the paint onto the fabric all around the cutouts. Advise him that a light spray will produce a striking bubbly effect and is less likely to seep under the stencil. (Another option is to press paint-coated sponges onto the fabric.)
Once the paint dries, remove the Con-Tact paper and the cardboard, then heat-set the design and launder the shirt according to the paint manufacturer's directions.