When I was 6 I remember having really scary thoughts all the time that our house would burn down in the middle of the night. Not so much a fear of death, more a fear of fire that little kids always had.
I also used to have a fear that a giant real life Mr Yuck sticker was hiding in my closet. Remember Mr Yuck? That sticker your mom put on all the household chemicals you weren't supposed to drink? I thought a 5-foot version with arms and legs was hiding in my closet, LOL.