I listened to a thing from a sex psychologist ages ago who talked about this. She said there was a connection between the developing arousal (sexual) and arousal (general emotional) that forms during the transition from childhood to adolescence, so there is commonly a connection formed between something the then-child has strong emotions toward, positive or negative, so a person can develop a sexual fixation on something beloved (mommy/daddy is perfect love personified. Dinosaurs are so frigging cool. etc.) or terrifying. (Mommy/daddy is mad. The monster is going to eat me all up. etc.)