I don't think it's prejudgemental at all! If I saw that father hanging around a park with children I would tell them to beware!! He has a Charlie Manson look to me.
I would never judge someone because they have tattoos or piercings or because they look different or have weird hair or different colored skin or whatever. Some of the best people I have ever met have been covered in tattoos.
Judging people by their appearance is just plain WRONG.
Besides, his father isn't the rapist murderer here...
JMHO