Why do young girls wear female swimwear?

Why do girls that are too young to have boobs wear swimwear that cover their chest? There's nothing there to cover. It doesn't seem there'd need to be a reason for it. I get that once their chest starts to develop, they need to cover it, but I cannot understand why a 5-year-old girl would need to have a swimsuit that is different from a 5-year-old boy's.

Why do young girls wear female swimwear?
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