Neighbours of a Californian couple accused of holding their children captive say there were signs something unusual was going on.

David and Louise Turpin have been charged with torture and child endangerment after 13 malnourished children and young adults were held in filthy conditions, some chained to furniture.

Their children, ranging in age from two to 29, are in a stable condition in hospital after being found dirty and malnourished.

CBS correspondent Thomas Wait told Chris Lynch he's spoken to locals who saw the children behaving strangely.

"One said she saw the children digging through a trash can outside, looking possibly for food."

The mother of the 13 malnourished children and young adults, was "perplexed" when deputies arrived at the family's Southern California home, a sheriff's official says.

The deputies had been summoned by a 17-year-old daughter who jumped out a window and called 911.

Riverside County sheriff's Captain Greg Fellows described the reaction of the mother, Louise Anna Turpin, 49, without elaborating. He said he did not know how the father, 57-year-old David Allen Turpin, reacted.

The situation at the home in Perris, southeast of Los Angeles, was discovered when the daughter escaped early on Sunday, Fellows said.

The teen, who was so small that deputies initially thought she was 10 years old, showed them photographs that led them to believe her story so they went to the home to check on the family, Fellows said.

The children, ages two to 29, are all believed to be the Turpins' biological offspring, authorities said.

Fellows said the investigation has so far found no indication of sexual abuse but that the conditions amounted to torture.

"If you can imagine being a 10-year-old and being chained to a bed ... I would call that torture," he said.

The family had lived in Perris since 2014, and deputies had never been to the residence previously for any reason, Fellows said.

Social workers had never visited either, said Susan von Zabern, director of the county Department of Public Social Services.

The parents were each held on $US9 million ($A13 million) bail and could face charges including torture and child endangerment.

State Department of Education records show the family home has the same address as Sandcastle Day School, where David Turpin is listed as principal.

In the 2016-17 school year, it had an enrolment of six with one student each in the fifth, sixth, eighth, ninth, 10th and 12th grades.

Neighbours in Perris, where modest but well maintained homes are tightly packed on suburban streets, said they were stunned by the arrests.

James Turpin, of Princeton, West Virginia, said Tuesday that he was surprised by the news reports about his son David. All 13 children are David's biological children. None are adopted, he said.

- additional reporting, AP