also: れいさいじ
child under one year old
Refers to an infant who has not yet reached their first birthday. Often used in medical, childcare, or statistical contexts.
Check the vaccination schedule for children under one year old.
This daycare accepts children from under one year old.
新生児 refers to a newborn, typically within the first 28 days of life, a narrower age range than ゼロ歳児.
Most common spelling using the loanword ゼロ for zero.
Numerical spelling; also readable as れいさいじ.
Kanji spelling with the reading れいさいじ; less common than ゼロさいじ.
Compound of ゼロ (zero) + 歳 (age, years old) + 児 (child). The reading ゼロさいじ is a straightforward combination; the alternative reading れいさいじ uses the native Japanese reading of 零.