Nowhere did the researchers associate this with "prejudice". The study isn't about making people feel bad about themselves, it's about identifying just how deep-rooted racism can be. At a point in your life where you're learning the most basic parts of being a functional human being (moving, communicating, etc etc), you're also learning to associate the color of the skin of people around you with comfort and safety. You can relax, nobody is saying these babies OR their parents are awful human beings.