Most kids never know real fear. Sure, they may be scared of the dark or think that there are monsters under their beds, but they always know that they have one or more parents less than a dozen feet away who will protect them from anything they can imagine happening.
Even as a child I knew what real fear was. I knew what it meant to be sure that you weren't going to survive to see another sunrise.
My father—not my biological father, who knows what happened to him—didn't tuck me in at night or tell me how much he loved me, but I always knew that he would do his level best to kill anyone who threatened me. For most little girls that wouldn't have been enough, but it was for me. That and he gave me a sister, an older sister who I knew would sacrifice almost anything to save me.
Of course I didn't understand all of that until I was much older. As a child I just knew that I felt safe when Geoffrey, my father, was around. The nights when he stayed in our house with me were the only ones where I didn't wake up screaming in the middle of the night.
It wasn't until later, after I found his journals, that I really learned how I came to live with him and understood why it was that he made me feel safe. I didn't need to fear the other monsters because I had my own personal monster a terrible, wonderful monster that I still don't understand completely, not even after he made the ultimate sacrifice to keep me safe.