We met Roxanne Castillo, eight, fishtailing her way through the schools of schoolchildren in front of the Shedd Aquarium. Her breezy sundress and hyperactive running shoes shouted “Let’s play!,” seemingly straining the limits of the “appropriate dress required” commandment permafixed to Shedd’s marble facade. Was Roxanne’s carefree costume a fish out of water? Our fashion ichthyologists reeled it in to get a cold-blooded fix on the markings.

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This fish story begins with a yellow-bellied sundress whose rippling skirt, breezy bodice, and brilliant color wriggle free from the confines of early children’s dress codes. Once upon a time babes of both sexes turned out in pure white puffery, as sexless and indistinguishable as guppy spawn. But once progressive educators suggested tots might differ from both adults and one another, kids’ clothes began to take on color (it used to be pink for Jacks, blue for Jills), relax in style, and mutate along the boy/girl divide. The postwar generation–baby-obsessed, convenience-happy, reverent of the doctors Spock and Freud–refined the pull-on, snap-shut, snuggly ease of kid couture and let its budding individualists choose their own stripes and plaids. Even Roxanne’s shrimpy version of running shoes, Velcro-scaled for small fry, are all wrap-and-go convenience.

But does the whole getup flounder, turning a cold shoulder on the stuffed-shirt concept of a dress code? According to research rehashed by Susan Kaiser in The Social Psychology of Clothing, uniforms promote herdlike groupthink. Dress codes, on the other hand, simply ask patrons to be on their best behavior. Leaving unstated what constitutes “appropriate” dress, unwritten codes rely on social animals to identify–and snub–the inappropriate.