Oh come off it. As IF these parents have never heard of Fred and Rose West.
Just because a murderer/murderers committed a crime, when you were just a kid, or before you were born, that doesn't mean you would not have heard of them.
Would you call your kids Ronnie and Reggie, or Myra if your name was Hindley, or Peter if your name was Sutcliffe, or Ian if your name was Brady, or Maxine if your name was Carr, or Harold if your name was Shipman? Most of them were decades ago, but everyone has heard of them.
My daughter was in the infants when the Ian Huntley/Maxine Carr thing happened with Holly and Jessica, and she wasn't born when Jamie Bulger was killed by Jon Venables and Robert Thompson, but she knows all about them all. Ditto, the Kray Twins, the Yorkshire Ripper, Jeremy Bamber, Ted Bundy, Charles Manson, Jeffrey Dahmer, Hindley and Brady, and many more.
Including multiple Victorian killers like Belle Gunness, Amelia Dyer, Jack The Ripper, The Lambeth Poisoner, and Mary Anne Cotton. . You don't have to have been born when something happened, to know about it. 🙄
Are you one of these people who would go on The Chase, and say to a question about something that happened 5 years before you were born 'before my time?'....... Just because something happened many years ago, or before you were born, that doesn't mean you would never have heard of it.