The term "flower child" originated in the 1960s and referred to a group of peace-loving people who came to be known as "hippies." In That Was Then, This is Now, by S.E. Hinton, one of the characters is referred to as a "true flower child," and it is a fitting description.

M & M Carlson is, indeed, a flower child. He wears a metal peace symbol around his neck, wears his hair long, and constantly wears a rather over-sized army fatigue jacket. Even more than his looks, however, M & M's actions are reflective of being a hippie or a flower child.

He is a peace-loving boy who is seen by others as being rather eccentric, though nearly everyone likes him because he has no desire for conflict. Just when he begins to feel too much of an outcast, he discovers a group of new hippie friends. They introduce M & M to marijuana, and now another aspect often associated with flower children and the hippie movement becomes a reality for the boy.

Eventually M & M runs away from home and moves in with another group of hippies; they soon give the thirteen-year-old a new nickname: "Baby Freak" because he is so young. Here M & M's drug of choice is the hallucinogenic drug LSD. LSD causes many dramatic changes in the boy's life and body. 

"M&M is just a kid.”
“Nothing bad happens to you when you’re a kid. Or haven’t you realized that?”

Plenty of things happen to this "kid," and they are all connected to his life as a flower-child hippie. M & M is, indeed, the epitome of a 1960s hippie and aptly named a "true flower child."