This is a very simple, but satisfying process I tried with 1st graders. All you need is a pencil, some stencils and watercolors. Over the years I have collected all kinds of stencils from garage sales, thrift stores, donations and catalogs. I have them all in a big box for kids to pick from. Sharpies are optional and can be used to trace over lines.
The first step is to use the stencils to draw shapes, write words and make designs. This is great for word practice and letter recognition for the kids. You could also tie in learning about shapes, patterns or colors.
Next, use watercolor paints to add color however you want. Sharpie markers can be used to define the shapes further with outlining.
I love how open-ended, personalized and creative this process can be.