I loved doing this in art class. Art With Mr. E: Line Design w/Shading - Grade Very cool, fun art shading project from Art With Mr. E. he's an elementary art specialist. Try this with your kids (but I think grown ups would enjoy this too).
How to draw and color an optical design. Add an illusion of depth in the design by using colored pencils coloring techniques. Mix and blend colors. Complete tutorial by artist and teacher Julianna Kunstler.
Fall trees with newsprint trunks. Maybe have kids look up images of trees on computers and discuss how they would change the art project to fit the season. ie What would the bare branches look like in art
A great thing about this project is it is JUST acrylic paint black Sharpies (love me some Sharpies) and scrap booking paper (Oh, and prepared canvases, Modge Podge and a Cricut machine) I think the last 3 items add a little cost