LOS ANGELES - The aunts of the 13 children who were found starved and held captive at home in California said the children's parents had always preferred to keep to themselves and had cut themselves off from the rest of the family.

One of the aunts also said her brother-in-law often made her feel uncomfortable and would sometimes watch her in the shower as "a joke".

The revelations came on Wednesday (Jan 17) as investigators combed through Louise and David Turpin's foul-smelling, filthy tract home east of Los Angeles.

Elizabeth Flores, one of Louise's sisters, said that for decades, she had begged to see her nieces and nephews even through videocalls, CNN reported.

But her sister and brother-in-law kept such a secret life that they wouldn't let her.

"When that happens for 20 years, and it was before the kids even were there, you don't think it's abnormal," Flores told ABC's Good Morning America.

"If it had been like two years ago that she cut us off, then we might think, wow, something's not right. But this has been going on before they even had children ... they were real private, and they didn't come around much."

Officers raided the family home in the small city of Perris, about 113km east of Los Angeles, on Sunday after one of the children escaped and alerted police.

Police said they found several of the couple's children, ranging in age from 2 to 29, "shackled to their beds with chains and padlocks in dark and foul-smelling surroundings."

On Wednesday, Louise and David Turpin were each charged with nine counts of torture and 10 counts of child endangerment. They were being held on US$9 million (S$11.9 million) bail, with an initial court hearing scheduled for Thursday.

Flores recalled how she once lived with the Turpins for two months when she was in college. The couple, who had a few children then, were strict but she said she "didn't see any abuse."

She said her brother-in-law made her feel uncomfortable - and he even used to watch her shower.

"If I went to get in the shower, he would come in while I was in there and watch me. It was like a joke," Flores said. "He never touched me or anything."

She said she never told anyone about it until now. "I was young. I was scared. I was in Texas, where I knew nobody," Flores said. "Now that I'm an adult, and I look back, I see things that I didn't see then."

Flores said her sister refused to let their father visit the family in 2012, even though he had already booked a flight.

"He got the ticket, he was going to surprise her, and he called her to tell him he was coming. And she told him not to come," reported CNN.

Flores said she was devastated to learn about the children's condition. Despite all this, she said she still loves her sister. "I want her to know that she's still my blood, and I love her," she said.

She also said she wants her nieces and nephews to "know they do have family... whether they know us or not."

Teresa Robinette, another sister of Louise, told NBC News that she was not aware of the conditions at the family's California home.

"We always thought she was living the perfect life," Robinette said of her sister. "She would tell us they went to Disneyland all the time. They would go to Vegas."

But she said she had expressed concerns about the children before. "I always made comments to Louise when I did talk to her, about, 'Gosh, they're so skinny.' And she would laugh it off: 'Well David's so tall and lanky. They're going to be like him.'"

Robinette broke down in tears when she heard about the children's alleged torture at home. "We are as hurt and shocked and angry and disappointed as everybody else," she said.

Family members and neighbours of Louise and David Turpin have offered little insight into the couple's possible motivations. Experts have said it may have been easier for the parents to shield their children from scrutiny because they were home-schooled.

"We have investigators on scene, combing through everything they can find for additional evidence," Riverside Sheriff's Deputy Mike Vasquez said on Wednesday. "They're trying to gather more information that may assist them in providing a full description of what was going on there.

"The whole house is a crime scene," he added, reported Reuters.

David Turpin's mother, Betty Turpin, said on Wednesday she was busy preparing paperwork and entering information into a computer to help her son. She said the family had engaged an attorney, who advised them not to speak about the case.