Media playback is unsupported on your device Media caption David Turpin (R) and his wife Louise Turpin (L) deny charges of torture

The parents accused of holding their 13 children in shackles at a California home have pleaded not guilty.

David Turpin, 56, and Louise Turpin, 49, are facing charges of torture, abuse and false imprisonment.

They were arrested after one daughter escaped from their home, where police later found some siblings chained to beds and severely malnourished.

The couple appeared in court hours after prosecutors detailed the horrific abuse allegations against them.

Riverside County District Attorney Mike Hestrin said the couple had allegedly punished their children by tying them up - first using ropes and later chaining them to their beds with padlocks.

He said the alleged punishments would last weeks or months, and intensified over time.

Prosecutors said circumstantial evidence showed the children were not released from their chains to go to the toilet.

The teenager who escaped and alerted police to the house where her siblings were held captive had been hatching a plan to leave for two years, Mr Hestrin added.

He detailed some of the gruesome allegations against the parents at a news conference on Thursday.

The shocking claims include:

The children were accustomed to frequent beatings, including strangulation

They were only allowed one shower a year

The children would stay awake all night until going to sleep at four or five in the morning and slept during the day

They were not allowed to play with any toys but many were found inside the house in their original packaging

If the children washed their hands above the wrist they were subjected to punishments, allegedly accused of "playing with water"

The Turpin parents allowed their children to eat only one meal a day but the parents would sometimes buy food, like pumpkin pies, and place it where the children could see it but not eat it

They have never seen a dentist and haven't visited a doctor in over four years

The children lack basic knowledge of life, and did not know who a police officer was

Media playback is unsupported on your device Media caption Shackled siblings: What we know about their lives

A grievous betrayal

James Cook, BBC News, Riverside, California

This case has sent waves of revulsion across the US and beyond, and the small courtroom was packed as the defendants appeared.

David and Louise Turpin were smartly dressed. They occasionally glanced at each other across a table weighed down by a copy of the California penal code and a sheaf of paper related to the case against them. A lawyer sat between them.

Mr Turpin, with a distinctive mop of grey hair, was chained around the waist, his stomach protruding from beneath the metal links. His wife's mouth was turned down in a glum expression.

The couple spoke only briefly and softly to confirm that they understood and accepted procedural details relating to their next hearing.

The charges they deny are among the most serious any parent could face: amounting to a grievous betrayal of their own children, a betrayal which prosecutors allege went on for years, if not decades.

The siblings themselves are said to be doing well but at least some of them have almost certainly suffered irreparable damage, both physical and mental from their ordeal.

The children, who are aged between two and 29 , have been treated in hospital since being freed on Monday.

The two-year-old was of normal weight but the other children were severely malnourished, authorities said.

The 12-year-old weighed as much as an average seven-year-old and the 29-year-old weighed only 82lb (37kg).

Several of the children have cognitive impairment and "neuropathy, which is nerve damage, as a result of this extreme and prolonged physical abuse", Mr Hestrin said.

Image copyright Reuters Image caption District Attorney Mike Hestrin said the couple chained their children as a form of punishment

Though little is known about their education, some of the children were able to read and write. Mr Turpin also registered a private school in their California home, known as Sandcastle Day School.

Police have obtained hundreds of journals that the children were allowed to write in and are looking through them for evidence.

Before moving to California, the family lived in Texas.

At one point, the parents allegedly lived in a different house from their children and would drop off food from time to time, officials said.

If found guilty of the dozens of charges against them, the couple face 94 years to life in prison, Mr Hestrin added.

Mr Turpin also faces one count of "lewd act on a child under 14 years of age".

Can anyone open a school at home in California?

The 13 children were found in an emaciated state in their filthy, foul-smelling house, police revealed earlier. Officers had at first thought all the children were minors but later realised some were frail and malnourished adults, they said.

Mr Hestrin said that when officers arrived, three of the couple's children were chained to their beds.

The charges against David and Louise Turpin: