This is a really good project that looks nice but also includes the kids. The first photo is what I did on a 2’x1.5′ canvas ($6 from Michael’s!). I used masking tape and star stickers and then painted over it with gray tempera paint. After it dried, the kids used red, blue and white paint to cover it. They did what I call “splat paint” (although I’m sure there is a more technical term). The kids dipped a paintbrush in red, white, or blue paint and “splatted” it against the canvas.
Here is the final product. Hopefully someone bids high!