More than 20 children are currently under the care of a child-welfare agency in California as investigations continue into a couple from the Los Angeles area. Authorities are examining whether they deceived surrogate mothers across the nation.

According to Arcadia police Lieutenant Kollin Cieadlo, a total of 15 children were taken from the couple’s luxurious residence in Arcadia following an abuse allegation in May, while six more children were found living elsewhere. The children range in age from 2 months to 13 years, with the majority being between 1 and 3 years old.

“We suspect one or two of the children were the biological offspring of the mother,” said Lt. Cieadlo. “Several surrogates have come forward, asserting that they acted as surrogates for these children.”

Silvia Zhang, 38, and Guojun Xuan, 65, are believed to be the legal parents of all the children, Cieadlo said.

They were arrested in May after a hospital reported that their 2-month-old infant had a traumatic head injury, the result of a nanny at the home violently shaking the baby, Arcadia police said. The child was not taken to the hospital for another two days.

Cieadlo said neglect charges were not formally pursued in order for an investigation to continue. The couple told police that they “wanted a large family,” the lieutenant said.

Zhang produced what appeared to be legitimate birth certificates, including some from outside California, that list her as the mother of the children, Cieadlo said.

He said the FBI is also part of the investigation. A spokesperson declined to comment when reached Wednesday by The Associated Press.

“I’m not familiar with how the surrogacy laws work,” Cieadlo said. “We need to do a much deeper dive.”

TV stations in Los Angeles quoted women who said they were surrogate mothers for the couple but that they didn’t realize other surrogates were also involved.

It wasn’t immediately clear if Zhang and Xuan had a lawyer who could speak on their behalf. Zhang did not immediately respond to an email seeking comment.

Business records with the California Secretary of State show a company called Mark Surrogacy Investment LLC was previously registered at the couple’s address. The most recent filing shows the business license was terminated in June.

The Los Angeles County Department of Children and Family Services, which removed the children, said it could not talk about its actions in a specific case.