Teenage step-brother molesting three year old sisters.
Mom needs support.
My step-son came to live with us at the age of ten after his mother found that he was performing sexual acts with his younger brother. My husband and I took him to counselling and the therapist told us he thought it was simply experimentation. Me, not being the natural parent, I went blindly along with the decisions my husband made. Step-son, we found out, had been introduced to sex by a cousin two or three years older than him. Mutual masturbation, from what I understand, was the most common interaction, I don't believe it went farther than that.