Final answer:
Childhood Amnesia is the condition where individuals have very few or no memories from the early years of their life.
Step-by-step explanation:
Xander's inability to recall memories before his third birthday party is a common condition known as Childhood Amnesia. It refers to the phenomenon where most individuals have very few or no memories from the early years of their life. This condition typically appears in adolescence, but there are rare cases where individuals have memories from before their tenth birthday.