I also am unable to recalll the majority of my childhood. I remember some things, but when I thought about it I realized I was remebering pictures I saw at a later age.
I blew it off, figuring my childhood was uneventful.
And if it wasn't - I don't think I want to know.
Maybe theres a good reason we block out memories.
It is not at all uncommon, and quite normal, for people to have this kind of scanty memory about childhood. You definetly should not jump to the conclusion that this because of some kind of trauma or sexual abuse. It is not the most likely explanation.
Its very difficult to retrieve memories by direct inquiry. The past is alive in another way than memories. It is alive in images that compete with your interpretation of interpersonal matters. If you are having troubles now, going to a therapist and working on those troubles, trying to sort out past images from current reality, is your best route to reconnecting with past experiences.