Most of the world have Scout (for boys) and Guide (for girls) groups. For some reason the USA did not take up the name 'Guides' and called them 'Boy Scouts' and 'Girl Scouts' instead.
(The original reason the Guides existed was that when Baden-Powell organised the first Scout rally on Brownsea Island, England, a number of girls turned up insisting that they were also Scouts and refused to leave, causing Baden-Powell to get a female relative to set up the Guides to accomodate them).
While the Scouts/Guides were divided by gender from the start, several other uniformed youth groups were not, such as the Falcons around Europe and the Woodcraft Folk in the UK, which recruited children of both sexes from the 1920's onwards. In some countries, e.g. the UK, the Scouts have now followed suit and admitted girls.