We've discussed Boy Scout uniforms and caps. . . so we should take a look at the Girl Scouts. "“Activities at the Girl Scouts Camp, Central Valley, New York. Line of the Girl Scouts waiting their turn to get their wash basins full of water at the water pipes.” July 21, 1918.

But I don't know much about them.

Girls Scouts on July 21, 1918.  Note the semi military uniforms, which pretty closely reflect the uniforms adopted by female auxiliaries of various types providing service during the Great War.

Except there's few hats in evidence.  Indeed, only one.

Is that a sailor's Dixie Cap?

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Addendum: 

I followed up on this thread with a new one actually on the evolution of Girl Scouts uniforms:

So, having babbled about Boy Scout uniforms, perhaps I should address the Girl Scouts as well.

And, in looking that up, I think I've come to the conclusion that the 1918 photograph that is featured in this photograph shows very early American Girl Scouts and Camp Fire Girls.  The white uniforms are probably Camp Fire Girls. The Camp Fire Girls were originally supposed to be a female version of the Boy Scouts and at this point in time there was a serious effort to unite the two organizations.  That effort ultimately fell apart, but my guess is that this camp had girls from both groups in anticipation of them being united.