Translation guide
The period of being a baby or very young child, or the early stage of development of something.
The period of life when someone is a baby or very young child.
The standard term for early childhood, roughly from ages 1 to 6. Used in formal and everyday contexts.
幼児期の経験は人格形成に大きな影響を与える。
Experiences in infancy have a great influence on personality development.
Specifically the infancy period when a child is still breastfeeding, typically under 1 year old. More clinical.
A casual, everyday way to say 'when (someone) was a baby'. Common in conversation.
赤ちゃんの頃の写真を見せて。
Show me pictures from when you were a baby.
Refers to childhood in general, often including infancy and early school years. More formal/literary.
The beginning or early period of something non-human, like a project, technology, or field.
General term for 'early stage' or 'beginning'. Works for most abstract or concrete things.
幼児期 (ようじき) covers early childhood broadly (1–6 years), while 乳児期 (にゅうじき) is specifically the nursing infant stage (under 1 year). Use 幼児期 unless you need to emphasize the baby stage.
乳児期の予防接種スケジュール
Infant vaccination schedule
幼児期 (ようじき) only applies to human children. For the early stage of a project or technology, use 初期 (しょき) or 黎明期 (れいめいき).
宇宙開発はまだ初期の段階だった。
Space exploration was in its infancy.
彼女は彼を幼児期から知っている。
She has known him since infancy.
Nutrition during infancy is very important.
彼は幼少期を海外で過ごした。
He spent his infancy/childhood abroad.
インターネットはまだ初期の段階だった。
The internet was still in its infancy.
Literally 'dawn period', used for the pioneering early days of a field or technology. Often in formal or written contexts.
人工知能の黎明期には、多くの基礎研究が行われた。
In the infancy of artificial intelligence, much basic research was conducted.
Literally 'cradle period', a more literary term for the infancy of a movement or idea. Rare in everyday speech.
この芸術運動はまだ揺籃期にある。
This art movement is still in its infancy.