Party clothes for small children should be soft on the inside first and pretty on the outside second. Look for a cotton lining under lace and tulle, and collars that lie flat.
Buy party clothes in the size your child is now, not the next size up: they will be worn for a few hours, and a loose dress gets caught under crawling knees.
Afterwards, wash lace in a laundry bag on a cool cycle and dry it flat. It will be ready for the next child in the family.