Flower child originated as a synonym for the children of Billy Ray Williams and his then wife Hazel Payne Williams who made and sold paper flowers while living on Haight Street, starting in the early 1960s. The two older daughters, Charlotte and Victoria, wore flowers in their hair while selling the paper flowers to tourists visiting the Haight Ashbury neighborhood. It eventually became a synonym for the idealistic young people who gathered in San Francisco and environs during the 1967 Summer of Love. It was the custom of "flower children" to wear and distribute flowers or floral-themed decorations to symbolize altruistic ideals of universal belonging, peace and love. The mass media picked up on the term and used it to refer in a broad sense to any hippie. Flower children were also associated with the flower power political movement, which originated in ideas written by Allen Ginsberg in 1965.
Scott McKenzie's rendition of the song "San Francisco (Be Sure to Wear Flowers in Your Hair)" was released in May 1967. The song was written by John Phillips to promote the June 1967 Monterey Pop Festival, and it urged visitors to San Francisco to "wear some flowers in your hair", in keeping with the festival's billing as "three days of music, love, and flowers":
If you're going to San Francisco,
be sure to wear some flowers in your hair...Summertime will be a love-in there.
If you come to San Francisco,
"San Francisco" became an instant hit (#4 in the United States, #1 in the U.K.) and quickly transcended its original purpose.
Summer of Love
After the January 14 Human Be-In organized by artist Michael Bowen (among other things, announcements told participants to bring flowers), as many as 100,000 young people from all over the world flocked to San Francisco's Haight-Ashbury district, Berkeley, and other Bay Area cities during the Summer of Love. in search of different value systems and experiences. The Summer of Love became a watershed event in the development of a worldwide 1960s counterculture when newly-recruited Flower Children returned home at the end of the summer, taking with them new styles, ideas, and behaviors and introducing them in all major U.S. and Western European cities.
Flowers and politics
The term achieved shades of political meaning when San Francisco Bay Area Flower Children gathered in Berkeley, California in April 1969 to participate in the planting of flowers, shrubs, grass, and trees during the building of People's Park. After authorities destroyed People's Park and installed an 8 ft (2.4 m) tall chain-link wire fence around its perimeter, planting flowers became a symbol of peaceful resistance.
In the October 21, 1967 march on the Pentagon, protesters were quickly surrounded by Federal troops. Actor George Harris put flowers in the barrels of the soldiers' guns. Photographer Bernie Boston snapped a picture which has become a familiar image of the 1960s antiwar movement.  Inspired by Harris' idealistic gesture, protesters at Kent State University three years later were still putting flowers in National Guardsmen's guns. 
- "Scott McKenzie's web site".
- "U.K. Number Ones 1960-69". Rockmine Archives.
- "Flowers, Guns and an Iconic Snapshot". In the Washington Post, March 18, 2007. Page found October 18, 2010.
- Allison Krause at the May 4 Archive. Page found October 18, 2010.
- 'Flower Child' in the American Heritage Dictionary
- Online Etymology Dictionary
- Official Information on the single, San Francisco