Formal or written term for a male child, often used in news reports, statistics, or official contexts. Contrasts with 女児 (girl).
See also: 女児
A boy suffered minor injuries in the accident.
He is the father of three sons.
Rare, formal, and somewhat old-fashioned when used for an adult male. More commonly encountered in set phrases or historical contexts.
A man should see through what he has decided.
A baby boy was born next door.
She safely gave birth to a boy.
男の子 is the everyday, casual word for a boy, whereas 男児 is a formal or literary term used in news and official writing.
counter for people
Compound of 男 (dan, 'male') and 児 (ji, 'child'). The kanji 児 is a common suffix in formal terms for children, as in 幼児 (young child) or 胎児 (fetus).