FWIW, there is something here Out West called The Strawberry Music Festival. It occurs twice a year (over the Memorial Day and Labor Day weekends). The site is beautiful: Camp Mather, just outside of Yosemite National Park. Camp Mather has acres of mountain meadows, pine forest and a lake on Hetch Hetchy.
The Music Festival has its own web page (mais oui) here.
Not only 3 days of camping, but a special kids' area & planned activities, a lake for swimming, a private 3-day radio station that broadcasts live the performances from the main stage, workshops, all-day and all-night jam sessions, usw.
The music is acoustic. Not always folk; the dreaded singer-songwriters show up too.
I've always wanted to go; haven't convinced the wife yet.