That's cause fear is encrypted in our genetics, to optimize our survival chances (if I can say so), unlike the tense sensation-and hence is a feeling we all can relate to, regardless of our age. There are already some means to bring fear in sims, like the good old thunderstorm, the movie 'sims of the dead', ghosts, bears... racoons! Also vampires and Nina Caliente... Like I'd love to see them add a fear list where you can put like 1 or 2 things a sim may find scary, and build on that, with different forces to the fear moodlet. Then why not adding a brave trait that would decrease the number/power of fears, while cowards would increase the strenght of their fears.