A Southern California couple with 21 children have been charged with conspiracy to commit child abuse and witness intimidation. Authorities allege that Silvia Zhang and Guojun Xuan deceived surrogate mothers and subjected the children, most of whom were born through surrogacy, to beatings and punishment.

The investigation began last year after a 2-month-old child was taken to a hospital with head injuries. Authorities arrested the couple Tuesday after searching their home in Arcadia, northeast of downtown Los Angeles.

Xuan also faces a felony child abuse charge, an accessory-after-the-fact charge and five counts of dissuading a witness. Zhang faces an accessory-after-the-fact charge and four counts of dissuading a witness. Both pleaded not guilty Tuesday and denied the allegations.

The couple’s attorney, Mitchell Krems, said Xuan did not abuse the children and argued that his unusually large family had drawn unfair scrutiny. Los Angeles County District Attorney Nathan Hochman described the alleged abuse at the home as severe.