Police say they lived in squalor for years, malnourished and deprived of contact with the outside world. Their parents are accused of torturing them.
Now on the road to recovery, David and Louise Turpin's seven adult children are turning to music to help them heal.
They've been learning to play the guitar and singing Tom Petty's "Learning to Fly" and John Denver's "Take Me Home, Country Roads" as a form of musical therapy, said Mark Uffer, the CEO of Corona Regional Medical Center, where the five women and two men have been recovering since they were taken from their parents' home in January. The six minor children were taken to a separate hospital.
Uffer said that all of the adult children "continue to be stable" and are making progress in their recovery. He declined to go into detail, citing privacy rules.
The medical center CEO first suspected the Turpins would benefit from musical therapy after he pulled out his acoustic guitar to entertain them, he said, and saw that it brought smiles to their faces. He played "Take Me Home, Country Roads."
They noticed the cover of his song book, and asked him, "Who is John Denver?"
But some of them recognized the song, he said, and started singing along -- "country roads, take me home, to the place where I belong."
"They all have good voices, beautiful voices," Uffer said. "And the tears started running down the nurses' faces."
So Uffer arranged for the Turpin siblings to receive new acoustic guitars.
The hospital CEO contacted Fender, and the company delivered the instruments to the hospital.
"Fender's local Corona employees offered a few of the guitars they make every day to the children, hoping it would help them heal," Fender CEO Andy Mooney in a statement to CNN.
Uffer and his staff leaned the guitars against a wall, labeled each with the name of one of the Turpin children, and put bows on them to make sure they looked like gifts.
They were excited to hold their guitars for the first time, Uffer said.
"The sight would have brought you to your knees," he said. "They all wanted to love you and hug you and say thanks. They are very appreciative."
Since then, the adult Turpin siblings have been learning to play the guitar and singing in a private room used for meetings, hidden from public view.
"Learning to Fly," written by Tom Petty and his close friend Jeff Lynne, seems to resonate with the Turpins, Uffer said.
"They fell in love with the song," he said. "They seem to understand it."
The lyrics are poignant, given what authorities say they have been through. "Well some say life will beat you down," the song goes, "Break your heart, steal your crown / So I've started out for God knows where / I guess I'll know when I get there."
Scientific research supports theories that music is healing. "The studies show that music can create profound neurochemical and biological changes, tangible, demonstrable ones," said psychologist Daniel Levitin, a professor emeritus at McGill University in Montreal, who specializes in neuroscience and music.
"Those changes can in turn affect things like mood, even the healing of physical wounds and psychological wounds as well," he said.
Levitin says that the brain responds to music, releases the chemical dopamine, which is associated with pleasure.
Learning to play an instrument or sing can propel traumatized children to express raw, deep-seeded emotions they have trouble talking about, said Dr. David Greenberg, a music psychologist with the University of Cambridge and City University in New York.
"Music is able to cross barriers, defenses," Greenberg said. "Trauma victims are able to communicate their emotions more rapidly."
Along with their new guitars, the Turpin children have also been given tuners, picks and cases. The late Petty and Denver themselves played Fender guitars, as did music stars from Bonnie Raitt to Jimi Hendrix.
Denver, an artist who exuded an aura of sunshiny American wholesomeness, co-wrote "Take Me Home, Country Roads" with Bill Danoff and his wife, Taffy Nivert Danoff.
The manager of Denver's estate said that he would have been thrilled to learn that the siblings are taking comfort in his music. "It's just phenomenal," said Brian Schwartz. "Can you imagine if 40 years ago you created something ... and somehow that would help someone who has been through a traumatic, horrific life event?"