Experiences in early childhood have a great influence on personality development.
幼児期に多くの言葉を覚える。
Children learn many words in early childhood.
幼児期 specifically denotes the early-childhood developmental stage (roughly ages 1-6), whereas 幼少 is a broader, more literary term for one's young years.
childhood amnesia; infantile amnesia
Compound of 幼児 (young child) and 期 (period, stage).