Decorate cookies with royal icing. For tree, use tip 3 and brown icing to pipe zigzag trunk. Use tip 16 and green icing to pipe zigzag branches. Sprinkle with nonpareils. Decorate girl and boy with tip 3. For girl, pipe in white dress, copper head and hands; pat smooth with finger dipped in cornstarch. Add zigzag cuffs, collar and dot hem in white. Outline and pipe jumper in green, shoes in black; add zigzag and dot trim in red. Outline hair in brown; pipe in bows and dot knot in red. For boy, pipe in white shirt, brown pants, copper head and hands and black shoes. Add outline straps in green, dot buttons in red and pull-out hair in yellow. For girl and boy, add dot eyes and string mouth in black, dot nose in copper.