also: きょうだい
noun
younger brother and sister
Refers to one's younger siblings collectively, specifically a younger brother and a younger sister. Not used for a single younger sibling.
彼は弟妹の面倒をよく見る。
He takes good care of his younger brother and sister.
弟妹がいる人は、小さい頃から我慢強く
People who have younger siblings tend to become patient from a young age.