* How do I know what size costume will fit me? There are two categories of costume sizes (adult and children) wherein you will be able to determine whether the costumes will fit you. The costume sizes available for adults include one or two fittings: standard or extra large fittings with different sizes variations. For children, costume sizes have three fittings, which are small, medium or large with different size variations appropriate within specific age limits. Always look for a costume with installed flexibility and adjustability features.