A couple accused of starving their 13 children and chaining them to beds had so many kids because it was God's calling on them, the children's grandparents are claiming.

David, 57, and Louise Turpin, 49, were arrested on Sunday and each charged with nine counts of torture and 10 counts of child endangerment after a 17-year-old, emaciated girl escaped their house east of Los Angeles, California, and called the police.

The 13 children ranging from aged 2 to 29 rarely left their dishevelled house and, when they did, they appeared small and pale and acted strangely, neighbours said.

Police said they found several of the children 'shackled to their beds with chains and padlocks in dark and foul-smelling surroundings'.

A statement from Riverside County Sheriff's Office said: 'The victims appeared to be malnourished and very dirty.'

Grandparents James and Betty Turpin described their utter shock at the allegations, saying their son David, daughter-in-law and grandchildren were a 'highly respected' good Christian family.

'God called on' the couple to have as many children as they did, the grandparents told ABC News.

The kids were given 'very strict homeschooling', they said, adding the children would memorise long passages of the Bible and some wanted to memorise it in full. The grandparents said they had not seen the children for four or five years but spoke regularly to their son, although not to his kids. The last time they saw the family they said they children 'looked thin' but they seemed like a 'happy family'.

Kimberly Milligan, 50, who lives across the street from the family, told Reuters that she only saw the infant in the mother's arms and three other children since she moved in across the street two years ago, describing them as small and pale.

'Why don't we ever see the kids?' Milligan said. 'In hindsight, we would have never thought this, but there were red flags. You never don't hear or see nine kids.'

Two years ago at Christmas time Milligan said she met three of the Turpin children and complimented them on the manger with a baby Jesus that they had outside their home. She said the children froze as if by doing so they could become invisible.

'20-year-olds never act like that,' she said. 'They didn't want to have a social conversation.'

Nicole Gooding, 35, who has lived in the neighbourhood for three years, said that the first time she saw the family was two months ago when the mother and children were cleaning up yard that was full of weeds and overflowing trash cans.

'I had never seen them at all until that day,' she said.

The parents, who are scheduled to appear in court on Thursday, are being held on $9 million bail, police said.

The police statement did not detail the parents' motive for holding the children and a police spokesman said he had no further details.

Six of the couple's children are minors, while the other seven are over 18.