Ok, Here goes...
I'm going to tell a story, and see if anyone can explain it to me.
I have this memory. I was in my parents car, my father was driving, and I was iin my mother's lap in the passenger seat. I was apparently too small to comprehend 'all' of their conversation, but I got some of it. They were talking about meeting my father's brother's and sisters for the 1st time. (he had been adopted as a child) Ok, next, we are at the door, I am in my mother's arms, my father knocks, and a girl comes to the door. I know she isn't grown, but she is much older than me. My father asks for 'someone', she says they aren't home, so he asks who else is there. She states another name, he asks to see that person. She, in turn brings a child to the door. He chuckles, and explains he needs to speak to an adult, and says he will return later. The girl closes the door and we walk away. My mother asks if maybe he should have told the girl who he was. He said no, that he didn't think that was a good idea. He needed to speak to an adult first. (Apparenly, it had been his sister).

Ok. Years later (for whatever reason) I mention this 'memory' to my mother. She looks at me with the blankest expression, and tells me that it is impossible that I remember that. When I ask her what was so impossible about remembering something from such a young age, she explains that it wasn't me in her arms that day. It was my sister, who died before I was born.

Any explanations?

Many memories can be bought out though hypnosis, I worked with many people bringing out childholld memories with them.

You may wish to find someone qualified and see if they can work with this memory and see if it is a first hand memory or something that was discussed and you "remember" the discussion as if it was you there.

Not putting any avenue aside, but this would be a good starting place

I think you saw this in your dream which really happened in real and when you recall your memory (which is a dream in fact) it turns out to be a real happening to you.
Quite often in our lives, when we recognize that we already know what has happened during this minute. For example I am sitting with my friend and we are discussing something and something reminds me that I've already seen all this before (that I am sitting with my friend and discussing on this day). That is actually we have seen all this in our dream and when we re-view all this, we recognize our dream.
Hope this is the answer.
What I have told you is not only my ownself experience but my friends have also told me that they also feel sometimes the same. This happens maybe once in a month or once in a year or more but it has happened to many persons I know.
What you tell to your mom that you were in her laps, actually you saw all this in your dream and that memory is so strong that it turns out to be happened in real.
This is only my opinion. You may agree or disagree.
Thanks.