A California couple have been arrested after police found their 13 children allegedly held captive at home, some "shackled to their beds with chains and padlocks".

David Allen Turpin, 57, and Louise Anna Turpin, 49, were held on charges of torture and child endangerment.

The couple's children - aged two to 29 - lived in Perris, 59 miles (95km) south-east of Los Angeles.

Officers were alerted by one of the victims, a 17-year-old girl.

The girl - who appeared to be "only 10 years old and slightly emaciated" - on Sunday managed to escape and call the emergency number using a mobile phone found inside the house, the Riverside Sheriff's Department said in a statement.

What did police find in the house?

Police officers later found "several children shackled to their beds with chains and padlocks in dark and foul-smelling surroundings".

The officers were "shocked" to discover that seven of them were actually adults aged between 18 and 29.

"The victims appeared to be malnourished and very dirty," the police said.

The couple's Facebook page contains numerous family photos 

They are now being treated in local hospitals.

The head of one of the hospitals, Mark Uffer, told Reuters news agency: "It's actually heartbreaking for the staff and it's unbelievable what you see."

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How did they hide their secret?

James Cook, BBC News, Perris

On Muir Woods Road there is no hint of the horror inside number 160.

This is a smart suburban home with three cars and a people carrier gleaming in the driveway. The curtains are drawn but a decorative Christmas star can be seen hanging in one window.

The estate is neat and the houses on the road are spacious but they are close together. It is difficult to imagine how a family could hide such an enormous dark secret here.

And yet that is exactly what seems to have happened.

Neighbours are now engaged in soul-searching about whether they should have spotted that something was awry.

No-one seems to know how long the siblings may have been held captive and, of course, no-one can answer the hardest question of all - why?

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What do we know about the family?

According to public records, the couple lived in Texas for many years before moving to California in 2010.

Mr Turpin has twice been declared bankrupt. At the time of his second bankruptcy he is said to have had a relatively well-paid job as an engineer at aeronautics and defence technology company Northrop Grumman.

However, with so many children and his wife not working, records suggest his expenses exceeded his income.

Mr Turpin's parents said that they had not seen the family for four or five years.

James and Betty Turpin told ABC they were considered a good Christian family in their community and that "God called on them" to have so many children.

The family's Facebook page shows numerous photos of them, apparently happy and smiling, some from events where David and Louise Turpin renewed their vows.

Many posts have comments from family or friends.

What about the children's education?

The grandparents said their grandchildren were home-schooled, but it is not entirely clear what that means.

On the California Department of Education website, Mr Turpin is listed as the principal of Sandcastle Day School - a private school operated out of his home.

The school was opened in March 2011, the website says. Six pupils are enrolled there, all in different grades.

In California, private schools operate outside the jurisdiction of the education department and most regulations. They are directly accountable to students and their parents or guardians, and the state has no authority to monitor or evaluate them.

Teachers at private schools in California also do not need to hold a valid state teaching qualification.

What do the neighbours say?

One neighbour told Reuters that the Turpin family "were the type that you didn't really get to know anything about them".

Neighbours said the Turpins rarely emerged from their home 

"You would never see them on visit, you would never see anyone come outside. All you would really see is that they go out and maybe do a grocery round. And that was about it," the neighbour added.

A neighbour from across the street, Kimberly Milligan, 50, told the Los Angeles Times they seemed strange and wondered why the children never came out to play.

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

She recalls on one occasion saying hello to the children but said they looked at her "like a child who wants to make themselves invisible".