Healthy childrenm, no matter where on the globe they live or what particular kind of language they speak, learn a native tongue. ... By about one year, they begin to speak recognizable words, and by the age of four or so they have mastered most of the exceedingly complex and abstract structures of their native tongues.
――英文和訳演習 上級篇 伊藤和夫 駿台文庫