child born within a year of another; children born in consecutive years
Refers to siblings born less than a year apart, or children born one after another with a small age gap. Often used in the context of family planning or describing sibling relationships.
うちの子は年子で、上がまだ一歳にならないうちに下が生まれました。
Our children are born within a year of each other; the younger one was born before the older one turned one.
年子の兄弟はよく双子と間違えられる。
Siblings born in consecutive years are often mistaken for twins.
Compound of 年 (とし, 'year') and 子 (こ, 'child'), literally 'year child'. The reading としご is a standard rendaku form.