Elyse is concerned because she cannot remember events before she was about 4 years old. this is called infantile

This is called infantile amnesia, also known as childhood amnesia.
Amnesia, as you already know, refers to the failure to remember things that happened, or people around you, or sometimes, in very severe cases, who you are. When it comes to infantile amnesia, however, it means that the child does not remember its earliest years.