Six-year-old fiona has no memory of being taken to the hospital when she was 2 years old. the rest of her family recalls what happened in vivid detail, but fiona only "remembers" what they have told her. her inability to remember this event is known as:

This event is known as infantile amnesia.
We tend not to remember the events that happened when we were too young, because our brains weren't developed enough for us to turn those short-term memories into long-term ones. Therefore, we forget what happened during our earliest years and may gain the recollection of some of those events if we are told by others.