The spiders my sister drew on the bottom of the top bunk bed were going to come alive and get me.
When I was about 4 or so we were parked outside a lady's house at night. My mom was inside and there was a plant casting a shadow in the window and I was convinced it was an alien and I was never going to see my mom again.
I was worried my eyes would catch on fire if I looked at the sun too much
I like to think I was a rational child... more so than I even am now :D