Kids who went through foster care frequently fail to remember entire years of their life, schools they attended, and families they lived with. There are multiple reasons for this, from trauma causing decreased working memory and formation of longterm memory during childhood to social factors such as lack of the same stability of and reminders of their life that a child who goes to one school for years and then has photos of themselves from that time to cement the memory will have. Most people do remember their life before 11 - the vast majority can name their school and neighborhood from back then without thinking, could tell you if they had a bike, if they liked school, etc. Some of these memories are indeed formed retroactively through stories, but they still exist.