Children costumed as flowers or insects for an event of the Wild Flower Preservation Society, Illinois Chapter, probably in a Chicago park, ca. 1920, hand-colored glass lantern slides by an unknown photographer, via The Field Museum Library Commons on flickr (all images here).
The Wild Flower Preservation Society of America was founded in 1902 with money given to the New York Botanical Garden by Olivia E. and Caroline Phelps Stokes. The funds were to be used for the protection of native plants.
The Society dissolved in 1933, but much of its work was taken up by the Garden Club of America and by another Wild Flower Preservation Society, founded in 1925 in Washington, D.C. (which seems no longer to exist).
Click here to see several more of the slides.