A California couple has been arrested on child abuse charges following an investigation into their use of surrogacy to build a family of 21 children. The arrests were reported by CNN, the Associated Press, ABC News and NBC News.

Most of the couple’s 21 children were born through surrogate mothers, according to NBC News. The network described the case as a “house of horrors” abuse investigation. Authorities began looking into the family’s home after concerns were raised about the children’s welfare.

Investigators are examining how the children were treated and whether the surrogacy arrangements were properly handled. Child welfare workers are now caring for the children, all of whom are minors.

The couple remains in custody. Officials have not released the names of the children to protect their privacy. Further charges are possible as the investigation continues.

The case has raised fresh questions about the oversight of surrogacy arrangements. Authorities say the probe is still in its early stages.

The investigation is also looking at the agencies that arranged the surrogacies. Officials say child safety drove every step of the probe.