I feel beauty pageants for children are a form of child abuse. It also attracts the wrong kind of people, mainly predators such as child molesters. It's a bad tradition and should be ended.
The difference is these pageants' sole purpose is to expose children's bodies for the most part to public viewing and to encourage girls to value their physical appearance over all else which leads to unhealthy beliefs and life choices later on. Putting on a swimsuit and going out for a swim is not intended for the purpose of people to see them in that level of dress so it's not the same thing as dressing in such a way for the primary purpose to be publicly viewed by others as in one of these beauty pageants.