Authorities in southern California on Tuesday are working to determine how a couple allegedly managed to keep their 13 children captive and on the verge of starvation inside their home without any apparent red flags in the community.

David Turpin and his wife Louise are in custody after authorities discovered "several children shackled to their beds with chains and padlocks in dark and foul-smelling surroundings," inside their home in Perris, Calif.

David Turpin’s parents told ABC News that they last saw the children five years ago. They recalled the children looking “thin,” but told the network that they seemed like a “happy family.”

The grandparents said when they would speak to David Turpin or his wife, the children were never available.

Authorities have planned a 10 a.m. PT press conference to update the public on new information in the case that started with a 17-year-old girl who “escaped” the house on Sunday to call 911.

She reported that her 12 brothers and sisters were being held by their parents, according to a press release from the Riverside County Sheriff’s Department.

The girl was “slightly emaciated.” Police believed she was 10 years old. The other victims appeared to be malnourished and very dirty. They were given food and drinks after they "claimed to be starving."

Their conditions were not immediately clear, and were sent to nearby hospitals to be treated.

Neighbors said they were shocked to learn about the conditions. One neighbor told the Press-Enterprise of Riverside that he didn’t even know children lived in the house.

Kimberly Milligan, 50, a neighbor who lived across the street, told the Los Angeles Times the few occasions in which she did see any kids come out of the house, they were very pale.

"I thought the kids were home-schooled," she said. "You know something is off, but you don't want to think bad of people."

Several other neighbors noticed red flags with the family – recalling an incident from a few months ago when some of the children were seen laying sod in the front yard late at night, the Times reported.

"I thought it was weird, but I'm the kind of guy that doesn't want to get in anybody's business," Gary Stein, 32, who lives on the street told the paper, adding that city officials were citing people with shabby lawns at the time.

Ivan Trahan, the couple’s bankruptcy lawyer, told The New York Times that they were a “very nice couple.” He said he never met the children, but the couple "spoke about them highly."

The Turpins previously lived in Texas before moving to California in 2010, the Los Angeles Times reported.

The couple apparently ran a public K-12 institution out of their home called Sandcastle Day School that opened in 2011, with David Turpin listed as the principal, according to the Times citing public records. In the 2016-17 school year it had an enrollment of six with one student in each of the fifth, sixth, eighth, ninth, 10th and 12th grades.

The Associated Press contributed to this report.