Tiered skirts are made by stacking three (or more) panels of fabric. Each panel is 1.5 times wider than the one above it. They are all approximately the same height, but an extra 1.5 inches has been added to the waistband (to allow you to fold over a waistband casing) and at the hem (allows for a 1.5 inch hem).
Each tier's top edge is gathered to be roughly the same width as the bottom of the tier above it. Starting with the bottom tier, attach each tier to the bottom of the tier above it.
Fold over the top to form a casing for a waistband. Thread through an elastic that is your child's waist measurement plus one inch.
Hem the bottom. Zigzag or serge any raw edges inside. Enjoy.