Using a makeup sponge, apply foundation in a color that matches the child's skin tone. Use more foundation than you would for "street" makeup. Blend the foundation at the jawline. Dust on lightweight, slightly shimmery powder so the makeup will stay put onstage.
Use a cream shadow on the lids -- pale gray or blue looks good on fair skin, while lilac complements darker skin. Choose a relatively muted color -- too bright and the child will look garish. Finish the eyeshadow with a dusting of powder to hold the color.
Line the eyes using a liquid eyeliner that matches the child's hair. For red hair, try a light brown. Extend the line on the top lash slightly past the eye, but don't turn it up. Finish the eyes with two coats of mascara a shade or two darker than the liner.
Use a cream blush in a peach or pale pink with shimmery tones to highlight the cheekbones. Blend into the foundation.
Apply lipstick two shades darker than the child's natural lip color. Begin by lining the lips with a lipliner pencil, then fill them in with lipstick. Avoid bright reds and bubblegum pinks, as these are too bright for children except on very large stages.