DENVER -- A Denver mother is on trial for sex assaults involving her own children.

"This is one of the sickest cases we've seen," said Lynn Kimbrough, a spokeswoman for the Denver District Attorney's Office.

The mother, who is not being identified by TheDenverChannel to protect the children's identities, faces 24 charges that include sexual assault on a child, sexual assault on a child by a person in a position of trust, and aggravated incest.

In opening statements, prosecutors said Tuesday that the mother dressed her son as a schoolgirl, put makeup on his face and then watched as his stepfather raped him. Prosecutors also said the boy's mother held down his younger sister while his stepfather raped her.

The prosecution said that sexual assaults began when the boy was 5 and when his sister was 7. The boy testified that he was abused for 10 years.

The woman's defense lawyer said that she was the victim of battered spouse syndrome and that she has since divorced her husband.

Jurors watched a videotaped interview in which the woman admitted to police that she helped her husband sexually assault her son and watched as he carried out the assaults.

Her lawyer said that she lived in constant fear of her husband, who shot her with a BB gun and hit her with an iron. She said her husband also physically and sexually abused her.

The alleged abuse came to light last summer when the woman was beaten with a flashlight and went screaming to a neighbor, who called police.

The son then stepped forward to tell police his story, which his mother corroborated in the videotape.

The son is now 18 and his younger sister is now 10. She testified Wednesday morning. A sister, therapist, and neighbor were also scheduled to testify for the prosecution.

The boy's stepfather will be sentenced later this month after pleading guilty to two counts of sexual assault on a child by a person in a position of trust.