The Desperate Housewives actress recently revealed in her memoirs that she was a victim of child abuse when she was 10 by an 18-year-old girl, who was a friend of the family.
In an interview for ABC's Nightline, Helen explained that she was unaware the experience was "wrong" at the time.
"It was definitely a choice, because it didn't need to be [in the book]," she said. "It happened one night where she told me, 'Come over here'. I didn't know that it was wrong, but I knew that it wasn't right because I wasn't supposed to tell anybody."
She added: "I think I was highly sexualised because I was in fifth grade and I had this experience. Because it feels good, you're like, 'OK, well this is supposed to be normal'. That's not normal for a 10-year-old to be seduced."
You Have No Idea: A Famous Daughter, Her No-Nonsense Mother, and How They Survived Pageants, Hollywood, Love, Loss (and Each Other) is co-written by Helen's mother Helen Williams and is released in the US today (April 17).
Helen said of her daughter's experience: "[I] had no idea that that had happened. But in retrospect, it kind of put into place some of her reactions during her pre-teen years."
Vanessa Williams's interview will air on Nightline on ABC tonight (April 17) at 11.35pm ET.
The actress recently signed on to join the ABC supernatural pilot 666 Park Avenue.