I came across a fascinating site artsalive.ca focusing on these very ideas of visually inspired composition with several lessons on color, shape, image, landscape. This site includes listening examples, art, lessons and background to various compositions. See http://www.artsalive.ca/collections/nacmusicbox/chronologique-timeline/index.php/en/connexionsmusicales-musicconnections/paysagevisuelsonore-landscapesoundscape/gl-eg-03
On a simpler note, have younger kids draw directly on the staff, e.g. mountains, or ocean waves, and where the mountain or ocean lines cross the staff, dot these intersections. These dots are shaped into notes. Tweak for rhythm, meter, etc.