A couple will be charged because their 10- and 12-year-old sons sexually molested three of their younger siblings, starting when one of the children was just one month old, authorities said.

Detectives believe the parents were aware of the abuse, but failed to report it to authorities and tried to handle it themselves by locking the older boys in a bedroom.

Prosecutors said one girl was just 2 years old when the abuse started in October 2002. The other girl was less than 8 months old. The sexual abuse of the boy allegedly began in December 2003, when he was just one month old, prosecutors said.

"This is one of the worst cases we have ever worked," Sheriff's Detective Craig Durrell told The Idaho Statesman newspaper.

The older boys could be charged in juvenile court for lewd conduct with a minor.

"The sad thing is, these kids, as much as they're suspects, they're victims," Durrell said.

The parents were to be arraigned Tuesday on four counts of felony child injury but a new hearing date was set for June 28, a court clerk said. At attempt to reach their attorney by phone late Tuesday afternoon was unsuccessful.

Seven of the couple's eight children have been in state custody since February, when investigators found evidence of abuse and neglect in their home, Durrell said. The other child has been in state custody since 1998.