I didn't study color theory until college, but it turns out color schemes aren't difficult for children to learn, if you start simply. For a recent monochromatic color scheme assignment, I had each student make a composition. They each started with their marker (a pencil would work fine for students without visual impairments) at the edge of the page and move it through curved straight, curly or zig-zag lines to another edge. They continued doing this with lines crossing over one another until the page was divided into large, medium, and small shapes.
Then they picked a color, and painted several of the shapes, throughout the composition in that color. Tints were made by adding the chosen color to white. Shades were made by adding black to the original color. the shades and tints of the color are spread throughout the picture plane to make it a strong composition, one that leads your eye around.