Spin art involves securing a piece of paper inside a machine that spins it while paint drips onto it. The result is a colorful, abstract piece of art. While spin art machines are available for purchase, it's possible to make your own from salad spinners available at discount and thrift stores for much less money. Cut paper circles that will fit exactly inside the spinner's basket. Place one in the spinner and drip different colors of paint onto the paper. Put the lid on the spinner and activate it for a minute or two. Remove the lid and the painting is ready to dry.
Colored sand is available in bulk from craft stores and makes a great material for a craft booth at a carnival. Cut the tips from squirt bottles and fill the bottles with sand. Fill them only half way so that an over-zealous child can't deplete your stock. While small plastic bottles in different shapes are available, collect clean, small baby food jars. Have children layer sand in the jar, making a pattern with hills and valleys. When the jar is full, put the lid on and instruct children not to shake it.
A face painting booth is one of the most popular attractions at a carnival. Make it more interactive by setting up a station with some mirrors. Provide carnival goers with paintbrushes and some face paints and let them decorate their own faces. Make up a sheet with design ideas for those who can't make up their minds and have a couple of face painters on hand for people who don't want to do it themselves. A couple of tubs of baby wipes help clean up mistakes.
If your carnival space has an area of flat black top, this is the perfect place to host a community craft project. Provide big pieces of sidewalk chalk and encourage carnival goers to add their artistic stylings to the blacktop. An alternative is to divide the blacktop into squares and sell sections for decoration to raise money. Have a photographer ready with an instant camera to take a picture of the finished art.