A California pair has been charged with multiple counts of abusing at least 14 surrogate-born children - some as young as two months old - and dissuading a witness.

"The number of children who were subjected to this alleged horrific abuse is unprecedented," Los Angeles District Attorney Nathan J Hochman said in a statement.

Guojun Xuan and Silvia Zhang, who US media describe as a couple, were arrested at their Arcadia mansion on Tuesday.

The pair pleaded not guilty at a Pasadena courthouse, the BBC's US partner CBS News reported.

Xuan, 66, and Zhang, 39, are accused of conspiring to subject 15 of the 16 children living in their home to repeated physical abuse, after 21 children were removed from their custody last year.

The pair ran their own surrogacy company and are accused of making false statements to at least two women who became surrogates, indicating that Zhang was struggling to conceive, according to the criminal complaint.

As of May 2025, Zhang maintained a spreadsheet that tracked 21 children, including those born to surrogates.

Officials said the investigation began that month when Zhang brought a two-month-old boy to the hospital with a head injury, telling medical staff that the baby had fallen from a bed.

The couple's lawyer Mitchell Krems said the allegation was a "mischaracterisation" based on the evidence he has reviewed, CBS News in Los Angeles reported.

Hospital staff informed law enforcement, and when police arrived at their home they discovered three different rooms called "learning centres" under the supervision of multiple nannies, which Hochman described as a "house of horrors".

The mansion allegedly had 32 motion-activated cameras which Hochman said were used by the couple to monitor the discipline given by the nannies.

Footage allegedly shows the nannies spanking, slapping or hitting the children.

One nanny, Chunmei Li, is accused of hitting the two-month-old baby who suffered the head injury two days before he was brought to the hospital.

Krems said Li was quickly fired, CBS News LA reported.

Li, 58, was previously charged with one felony count of child abuse under conditions likely to cause great bodily injury or death. Hochman said she was on the run with a $105,000 (£88,800) warrant for her arrest.

In July 2025, the couple's home was first raided by authorities, who took 21 children into state custody.

Arcadia Police Department said at the time the couple's house was first raided that the children ranged in age from two months to 13 years old, but most were between one and three years old.

Fifteen of the children were taken from the couple's home while six others were living elsewhere and also later taken into custody.

Krems said his client Xuan was innocent.

"He is being targeted for exercising his constitutional right to have a large family," CBS News quoted the lawyer as saying.

Investigators believe the surrogate mothers were from around the country and they were unaware they were carrying embryos for the couple at the same time.

Melissa Brisman, the attorney for two of the surrogates, told CBS News: "This is wonderful news that people will be held responsible for their actions and there will be consequences if you abuse the surrogacy system".

If convicted as charged, Xuan faces a possible maximum sentence of 17 years and four months in state prison, while Zhang faces up to 11 years and eight months. Li faces up to 12 years.