A cape can be fashioned easily from black material or a black sheet. Put socks on, then wrap red tape around from bottom to top, to create a striped sock effect. Socks can be dyed green first if you prefer. You may also use craft paint for the stripes, but tape is faster and easier. Carry broom and wear witch's hat.
Paint face green and add dark smudges around eyes and mouth.
Use black lipstick and nail polish to finish the look. After child is dressed, tie red material around neck as a neckerchief. Slick child's hair back, paint face white. Put teeth in then apply fake blood around corners of mouth. Smudge dark circles around eyes.